Source: http://grammar.yourdictionary.com/style-...words.html

Accept vs. Except
Accept (verb) - to receive

I accepted all my birthday gifts with gratitude.
Except (conjunction) - apart from; otherwise than; were it not true

When Susan travels, she packs everything except the kitchen sink.
Affect vs. Effect
Affect (verb) - to have an effect on; influence; produce a change in; to stir the emotions

The dog's death affected his owners.
Effect (noun) - anything brought about by a cause or agent; result

The new speed limit law had little effect on the speed of the motorists.
All Intensive Purposes vs. All Intents and Purposes
"All intensive purpose" is an incorrect use of the phrase "all intents and purposes."

"All intents and purposes" is a phrase that means "for all practical purposes" or "under most usual situations."

For all intents and purpose, she planned to buy the refrigerator but still wanted to check the reviews.
A Lot vs. Allot
A lot (noun phrase) -many

A lot of people came to the party.
*"A lot" is always two separate words. "Alot" is not a real word.

Allot (verb) - to distribute, give or assign

Fifteen minutes were allotted to each of the speakers at the conference.
Allusion vs. Illusion
Allusion (noun) - an indirect reference

The Austin Powers movies often make allusions to the James Bond films.
Illusion (noun) - a false idea or conception; belief or opinion not in accord with the facts; an unreal, deceptive, or misleading appearance or image

The magician created the illusion that he was levitating.
Awhile vs. A While
Awhile (adverb) - for a while; for a short time

The guests planned to stay awhile.
A while (noun) - for a short time; when while is used as the object of the preposition (for a while) then the "a" is separated from the "while"

The guests planned to stay for a while.
Bad vs. Badly
Bad (adjective) - not good

Your feet smell bad.
Badly (adverb) - not well; in a bad manner; harmfully; incorrectly; wickedly; unpleasantly

Charlotte plays tennis very badly.
The people involved in the accident were badly hurt.
*Here, a note. Adjectives generally describe nouns, so even if you use the word “bad” following a verb in a sentence, if it’s meant to describe the thing itself, then use the adjective. “Bad” here means the same as “rotten,” “rancid” or “stinky,” all of which are adjectives. If you can replace “bad” with another adjective and still have a sentence that makes sense, then you know that “bad” was the correct choice. Adverbs often describe the manner in which something is done. To say, “your feet smell badly” is to say that your feet are inhaling through the nose and perceiving odors, and that they’re going about it all wrong.

Borrow vs. Lend
Borrow (verb) - to take or accept something for a short time with the intention of returning it to its rightful owner

May I borrow a pencil, please?
Lend (verb) - to give something for a short time with the intention of getting it back

Would you please lend me a pencil?
Breath vs. Breathe
Breath (noun) - air taken into the lungs and then let out

Take a deep breath.
Breathe (verb) - to inhale and exhale

Just calm down and breathe.
Butt Naked vs. Buck Naked
Butt Naked is a phrase that means to be without clothes.

The baby tore off his diaper and ran around the house butt naked.
Buck Naked is a phrase that also means to be naked and without clothing.

The baby tore off his diaper and ran around the house buck naked.
*Note - Neither of these phrases is incorrect. The term buck naked may derive from the term buckskin, that which hides are fashioned. However, neither term has much etymological backing for one being more correct than another.

Cache vs. Cash
Cache (noun) - a safe place to store supplies; anything stored or hidden in such a place

The hikers found a cache with some cash and jewels.
Cash (noun) - money, coins, bills; currency

ATM machines dispense cash.
Chomp at the Bit vs. Champ at the Bit
Chomp at the bit - an over used and incorrect form of "champing at the bit"

Champ at the bit (idiom) - ready or anxious; eager to be going or moving along.

The kids were champing at the bit to see the newest Harry Potter movie.
Complement vs. Compliment
Complement (noun) - that which completes or brings to perfection; (verb) - to make complete

Red wine is a nice complement to a steak dinner.
Compliment (noun) - something said in admiration, praise, or flattery; (verb) - to pay a compliment to; congratulate

She gave me a nice compliment when she said I looked thin.
Comprise vs. Compose
Comprise (verb) - to include; to contain; to consist of; to be composed of

The state of North Carolina comprises 100 counties.
Compose (verb) - to form in combination; make up; constitute

One hundred counties compose the state of North Carolina.
Desert vs. Dessert
Desert (verb) - to forsake or abandon; to leave without permission; to fail when needed

Soldiers should not desert their posts.
Desert (noun) - dry, barren, sandy region

The largest desert in the world is the Sahara.
Dessert (noun) - a sweet course served at the end of a meal

Fruit makes a healthy dessert after lunch or dinner.
Done vs. Did
Done (adjective) - completed; sufficiently cooked; socially acceptable

Done (verb) - the past participle of do

After an hour, the roast was done.
Did (verb) - past tense of do

The children did not want to leave the playground.
Elicit vs. Illicit
Elicit (verb) - to draw forth; evoke

The teacher elicited answers from the students.
Illicit (adjective) - unlawful; illegal

The teacher discovered illicit drugs in a student’s desk.
Fair to Midland vs. Fair to Middling
Fair to midland - an incorrect use of the phrase "fair to middling"

Fair to middling (phrase) - something that is moderate to average in quality

The temperature was fair to middling today.
Had Bought vs. Had Boughten
Had Bought (verb) - the past perfect tense of the verb buy

The teacher had bought Christmas presents for all of students early in the year.
Had Boughten - incorrect usage of the past perfect tense

Hone vs. Home
Hone (verb) - to sharpen; to yearn or long for; to grumble or moan

Practicing the piano daily is a good way to hone your skills.
Home (noun) - dwelling; place where a person lives

After the long drive, we were all ready to be home and asleep.
Idiosyncrasy vs. Idiosyncracy
Idiosyncrasy (noun) - any personal peculiarity or mannerism; individual reaction to food or drug.

Twins have idiosyncrasies, which often help to distinguish one from the other.
Idiosyncracy is a misspelling of idiosyncrasy.

Imitated vs. Intimated
Imitated (verb) - past tense of the verb imitate, which means to seek to follow the example of; impersonate; mimic

The toddler imitated the dog by crawling on hands and knees and barking.
Intimated (verb) - to make known indirectly; to hint or imply

The pirate intimated that he knew where the treasure was buried.
In a Sense vs. In Essence
In a sense (idiom) - in a way; in one way of looking at it

In a sense, computers have been a boon to society.
In essence (idiom) - by nature; essentially

The cat is, in essence, quiet and timid.
In One Foul Swoop vs. In One Fell Swoop
In one foul swoop - an incorrect use of the phrase "in one fell swoop"

In one fell swoop - a phrase meaning "all at once"

In one fell swoop, the toy was demolished by the child.
Its vs. It’s
Its (possessive pronoun) - of, belonging to, made by, or done by it

The dog will only eat its food when I am also eating.
It’s (contraction) of it + is

It’s a very strange dog.
I Could Of vs. I Could Have
I could of - an incorrect use of the verb phrase could have; when written as a contraction "could've" sounds like "could of."

I could have - is the past perfect tense of the verb could

I could have gone to the play, but I had to study that night
I Should of vs. I Should Have
I should of - an incorrect use of the verb phrase should have; when written as a contraction "should've" sounds like "should of."

I should have - is the past perfect tense of the verb should

I should have gone to the play instead of study because I failed my test anyway.
I Would Of vs. I Would Have
I would of - an incorrect use of the verb phrase would have; when written as a contraction "would've" sounds like "would of."

I would have - is the past perfect tense of the verb would

I would have gone to the play except my car wouldn't start.
Lead vs. Led
Lead (noun) - a heavy, soft, malleable, bluish-gray metallic chemical element used in batteries and in numerous alloys and compounds

I think it was Mrs. White in the billiard room with the lead pipe.
Led (verb) - past tense and past participle of the verb "to lead"

The two coaches have each led their teams to numerous championships.
Lose vs. Loose
Lose (verb) - to become unable to find; to mislay; to fail to win or gain

Did you lose your glasses again?
How many games did your team lose last season?
Loose (adjective) - not tight; giving enough room

I’ve lost twenty pounds, and now these jeans are really loose.
More/Most Importantly vs. More/Most Important
More/most importantly - a phrase used often in writing to show emphasis; however, many grammarians insist that this is not correct usage. The adverbial ending of -ly is not needed.

More/most important - this phrase should be used instead

The most important part of story is the ending.
Passed vs. Past
Passed (verb) - past tense of the verb "to pass"

I think we passed the store. Let’s turn around and go back.
Past (adjective) - of a former time; bygone; (noun) - the time that has gone by; days, months, or years gone by

In the past, I’ve gotten lost a lot, but this time I know where we are.
Precede vs. Proceed
Precede (verb) - to be, come, or go before in time, place, order, rank, or importance

The election of a new president precedes his inauguration.
Proceed (verb) - to advance or go on, especially after stopping

After your first assignment has been completed and approved, you may proceed to the second one.
Principal vs. Principle
Principal (noun) - a governing or presiding officer, specifically of a school; (adjective) - first in rank, authority, importance, degree, etc.

The student’s parents had to have a meeting with the principal.
Principle (noun) - a fundamental truth, law, doctrine, or motivating force, upon which others are based

The student’s parents thought that they had instilled stronger moral principles in their son.
Seen vs. Saw
Seen (verb) - past participle of the verb see; must be used with the verbs has, have, or had

I have seen the movie three times.
*Note: I seen the movie three times is not correct though it is commonly used in spoken language.
Saw (verb) - past tense of the verb see

I saw the movie yesterday.
Sell vs. Sale
Sell (verb) - to give up, deliver or exchange for money

People who move often sell unwanted items instead of packing them.
Sale (noun) - the act of selling; the work, department, etc. of selling

After Christmas sales always bring in the bargain shoppers.
Site vs. Sight
Sight (noun) - something seen, a view, field of vision

She was a sight for sore eyes.
Site (noun) - a piece of land considered for a specific purpose

The corner lot was a perfect site for the new shopping center.
Spitting Image vs. Spirit and Image
"Spitting image" is a phrase that means exactly like. The first known use in writing of this phrase was in 1901.

Karen is the spitting image of her mother.
"Spirit and Image" - There is some speculation that the "spit" in the phrase "spitting image" came from the word "spirit" in the phrase "spirit and image." However, there is no etymological basis for this belief since the phrase "spirit and image" used in reference to an exact likeness is not found in writing. The terms "spit," "spit and image," and "dead spit" have all been found to refer to a likeness since the 1800's.

Stationary vs. Stationery
Stationary (adjective) - not moving or not movable; fixed or still

I rode the stationary bike at the gym for an hour.
Stationery (noun) - writing materials; specifically, paper and envelopes used for letters

My grandmother has given me a lot of stationery over the years. I think she wants me to use it to write her.
Taut vs Taunt
Taut (adjective) - tightly stretched; showing strain; tidy or well-disciplined

The taut rope held the luggage to the roof.
Taunt (verb) - to reproach in scornful or sarcastic language; to drive or provoke

The home team taunted the visitors with cheers every time the visiting team made an error.
Than vs. Then
Than (conjunction) - used to introduce the second element in a comparison

My right foot is bigger than my left foot.
Then (adverb) - at that time; next in order; (adjective) - of that time; (noun) - that time

Take off all your clothes first. Then get in the shower.
Emily drove up to New York with her then boyfriend, Nick.
Let's wait until we're hungry; we can decide what we want to eat then.
Their vs. There vs. They’re
Their (adjective) - of, belonging to, made by, or done by them

They were proud of their work.
There (noun) - that place or point

Just put it over there.
They’re (contraction) of they + are

They’re going out to dinner tonight.
To vs. Too vs. Two
To (preposition) - in the direction of and reaching; as far as; to the extent of

I’m going to Baltimore.
Too (adverb) - in addition; as well; besides; also; more than enough; superfluously; overly; to a regrettable extent; extremely

I’m going to Baltimore, too.
I'm too busy. I can't go to Baltimore.
Two (adjective) the number 2

I have two jobs.
Your vs. You're
Your (adjective) - belonging to you

Is this your dog?
You're (contraction) - you are

You're a great mother!
Who vs. Whom
Who (subject pronoun) - what or which person or persons; the person or persons that, or a person that (used to introduce a relative clause)

Who is going to the party with you?
Whom (object pronoun) - what or which person or persons; the person or persons that, or a person that (used to introduce a relative clause)

With whom are you going to the party?