ill
34 synonyms and 7 antonyms for ill, grouped by meaning and by how common each one is.
Adjective — Unwell or in poor health; sick.
Synonyms
Everyday swaps
Common words most readers know — safe in any writing.
Less common
Still standard English, but they carry more weight.
Rare, literary or technical
Precise, but they will stand out — check the sense before using one.
Antonyms
How to use ill
The word patterns that sound natural to a native speaker.
Etymology
From Old Norse illr, "bad, evil," related to Danish ilde and Swedish illa.
Full origin of ill →Frequently asked questions
What does “ill” mean?
The word “ill” means unwell or in poor health; sick. In plain terms, most commonly means "sick," but as an adverb/prefix it also means "badly" (ill-advised, ill-timed).
How do you pronounce “ill”?
“Ill” is pronounced ihl (/ɪl/ in IPA).
How do you use “ill” in a sentence?
Here is “ill” used in a sentence: “She stayed home from work because she felt ill.”
What is another word for “ill”?
Words with a similar meaning to “ill” include bad, mal-, crank, crook, green about the gills and icky.
What is the opposite of “ill”?
The opposite of “ill” — its antonyms — are fine, hale, healthy, in good health and well.
What part of speech is “ill”?
Depending on how it is used, “ill” can be an adjective, an adverb and a noun.
Where does the word “ill” come from?
The word “ill” comes from Old Norse. From Old Norse illr, "bad, evil," related to Danish ilde and Swedish illa.
Is “ill” a common word?
“Ill” is a very common word in modern English, usually learned at around the A2 level.
What is the difference between ill and sick?
Ill and sick both mean unwell, and in most contexts they are interchangeable. British English tends to prefer "ill" for being unwell, reserving "sick" for the sense of vomiting; American English uses "sick" more broadly for any illness. "Ill" can also sound slightly more formal or more serious.
Does ill always mean sick?
No. Besides meaning unwell, "ill" can mean bad, harmful, or hostile, as in "ill will," "ill effects," "ill-advised," or "speak ill of someone." As an adverb it means badly, as in "ill-equipped." As a noun, "ills" are troubles or problems. The unwell sense is simply the most familiar.
Is ill formal or informal?
"Ill" is neutral to slightly formal and works in both everyday and professional writing. In British English it is the standard word for being unwell, where American English often prefers "sick." It fits comfortably in phrases like "seriously ill" or "taken ill," carrying a measured, matter-of-fact tone.
What is the opposite of ill?
When "ill" means unwell, its opposite is "well" or "healthy" — you might say someone is "well again" after recovering. Other antonyms include "fit," "sound," and "in good health." When "ill" means harmful, as in "ill effects," the opposite shifts to "good" or "beneficial."