What does ill mean?
Ill primarily means unwell or suffering from a health problem, as in 'the child became ill during the night.' It can also describe something harmful, undesirable, or badly conceived, such as an 'ill decision' or 'ill health.' The expression 'ill at ease' means uneasy or uncomfortable, while 'think ill of' means to regard someone or something unfavourably. In formal and literary contexts, ill can function as an adverb meaning badly or in an unsatisfactory manner. Although the adjective is the most familiar use, the word is flexible in meaning because its basic idea has long involved both physical condition and moral or practical quality. It remains common in British and American English, with 'sick' often being preferred in casual conversation when someone is unwell.
Unwell or suffering from an illness; also, bad, harmful, undesirable, or causing discomfort.
"The doctor said that the patient was seriously ill."
When meaning unwell, ill is somewhat more formal than sick or unwell.
Badly or in an unsatisfactory manner.
"The proposal was ill received by the committee."
This use is especially common in formal, literary, and idiomatic expressions.
From Old Norse illr, a word that survives in English through phrases such as 'fall ill' and 'ill at ease'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does ill come from?
The word comes from Old Norse illr, meaning bad, harmful, or unwell, and entered English during the medieval period. Its Germanic ancestry is also reflected in related forms such as evil. English later developed the noun illness and the now-archaic noun illth, the opposite of wealth or well-being, from the same older word.
Related word forms
How ill is actually used
Ill is a slightly more formal or literary alternative to unwell in the sense of being in poor health. In phrases such as 'ill at ease' and 'think ill of', it describes a condition, attitude, or reputation rather than physical illness.
Easily confused with ill
Both can mean unwell, but sick is more common in everyday speech and is also used specifically for nausea, illness, or distress.