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• ill
  ill

  adjective

  of unsound physical or mental health; unwell; sick.
• I'll
  I'll

  contraction of I will.
• ill.
  ill.

  abbreviation

  illustrated.
• Ill.
  Ill.

  abbreviation

  Illinois.

ill

¹ American  

[il] / ɪl /

adjective

worse, worst, iller, illest

1. of unsound physical or mental health; unwell; sick.

   She felt ill, so her teacher sent her to the nurse.

   Synonyms:

   afflicted, diseased, ailing, unhealthy

   Antonyms:

   healthy, well

2. objectionable; unsatisfactory; poor; faulty.

   ill manners.

3. hostile; unkindly.

   ill feeling.

4. evil; wicked; bad.

   of ill repute.

   Synonyms:

   iniquitous, wrong

   Antonyms:

   good

5. unfavorable; adverse.

   ill fortune.

6. of inferior worth or ability; unskillful; inexpert.

   an ill example of scholarship.

7. Slang. great; amazing.

   His mom is the illest cook.

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noun

1. an unfavorable opinion or statement.

   I can speak no ill of her.

2. harm or injury.

   His remarks did much ill.

   Synonyms:

   misery, affliction, pain, hurt

3. trouble, distress, or misfortune.

   Many ills befell him.

   Synonyms:

   calamity

4. evil.

   to know the difference between good and ill.

   Synonyms:

   depravity

5. sickness or disease.

   Synonyms:

   affliction, illness

adverb

1. in an ill manner.

2. unsatisfactorily; poorly.

   It ill befits a man to betray old friends.

3. in a hostile or unfriendly manner.

4. unfavorably; unfortunately.

5. with displeasure or offense.

6. faultily; improperly.

7. with difficulty or inconvenience; scarcely.

   Buying a new car is an expense we can ill afford.

idioms

1. ill at ease, socially uncomfortable; nervous.

   They were ill at ease because they didn't speak the language.

I'll ² American  

[ahyl] / aɪl /

1. contraction of I will.

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ill. ³ American  

abbreviation

1. illustrated.

2. illustration.

3. illustrator.

4. most illustrious.

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Ill. ⁴ American  

abbreviation

1. Illinois.

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ill ¹ British  

/ ɪl /

adjective

1. (usually postpositive) not in good health; sick

2. characterized by or intending evil, harm, etc; hostile

   ill deeds

3. causing or resulting in pain, harm, adversity, etc

   ill effects

4. ascribing or imputing evil to something referred to

   ill repute

5. promising an unfavourable outcome; unpropitious

   an ill omen

6. harsh; lacking kindness

   ill will

7. not up to an acceptable standard; faulty

   ill manners

8. unable to relax; uncomfortable

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noun

1. evil or harm

   to wish a person ill

2. a mild disease

3. misfortune; trouble

adverb

1. badly

   the title ill befits him

2. with difficulty; hardly

   he can ill afford the money

3. not rightly

   she ill deserves such good fortune

Ill. ² British  

abbreviation

1. Illinois

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I'll ³ British  

/ aɪl /

contraction

1. I will or I shall

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ill More Idioms  

More idioms and phrases containing ill

• get sick

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Grammar

See well ¹.

Usage

What are other ways to say ill? The adjective ill is defined as “evil; wicked; bad.” However, it’s not used in exactly the same way as any of those synonyms! Learn the difference among these terms on Thesaurus.com.

Related Words

Ill, sick mean being in bad health, not being well. Ill is the more formal word. In the U. S. the two words are used practically interchangeably except that sick is always used when the word modifies the following noun: He looks sick ( ill ); a sick person. In England, sick is not interchangeable with ill, but usually has the connotation of nauseous: She got sick and threw up. sick, however, is used before nouns just as in the U. S.: a sick man.

Etymology

Origin of ill¹

1150–1200; Middle English ill ( e ) (noun and adj.) < Old Norse illr (adj.) ill, bad

Origin of ill.³

ill. ( def. 4 ) < Latin illustrissimus

Explanation

If you're ill, you're unwell, or sick. Being ill is a good excuse for missing work or school. You might get ill after being sneezed on by someone with a cold; or eating street food in a foreign country; or for no reason that you can point to. People can be mentally ill as well as physically ill, from depression or anxiety among other ailments. Ill can also mean "bad" in various ways, including when you suffer ill effects from going too long without sleep, or exercise ill judgment when you buy $500 worth of lottery tickets.

Example Sentences

She patented it in 1951, and that year sold the rights to her patent for $1 million to Keko Corp. of Kankakee, Ill.

From The Wall Street Journal • Apr. 9, 2026

The Terminally Ill Adults Bill was passed by 314 votes to 291 in the House of Commons - but will need to go through the Lords before becoming law.

From BBC • Jun. 21, 2025

The couple used donations they’d been offered from their church to pay for the drive to California from Robbins, Ill.

From Los Angeles Times • Nov. 10, 2024

They’ve mostly relied on players such as Rhattigan was when he entered West Point out of Neuqua Valley High in Naperville, Ill.

From Seattle Times • Nov. 10, 2023

Ill And they inevitably move into more and more, worse and worse, illegality and immorality.

From "The Autobiography of Malcolm X" by Alex Malcolm X;Hailey

Related Words

• abuse
• affliction
• ailment
• disease
• disorder
• evil
• illness
• infirmity
• malady
• malaise
• misery
• pain
• sickness
• suffering
• syndrome
• trouble
• woe