In his latest word grammar article, Tim Bowen makes sure you won’t be ill-informed or ill-prepared.
Apart from its main use as an adjective, ill can also function as an adverb, a prefix and, more rarely, as a noun.
Apart from its adjectival meaning of ‘not healthy’, ill can also mean bad or harmful but is only used in the pre-nominal position in this sense, as in ‘The fish didn’t taste fresh but we suffered no ill effects’.
As an adverb, ill is a rather formal alternative to badly, as in ‘I’m afraid you have been ill-informed’. It is also used in the expression can ill afford something / to do something, used to say that someone should definitely not do something because it will cause problems, as in ‘We can ill afford another disagreement with the organization that pays our wages’.
The prefix ill- is used with a number of past participles, again with the sense of badly or poorly, as in ‘He has made a number of ill-considered decisions during his career but this is probably the worst’ or ‘The poor quality of the teaching during the course meant that we were ill-prepared when it came to tackling the rigours of the written exam’.
As a noun, ill is normally used in the plural to refer to problems or difficulties, as in ‘Some people seem to believe that a change of government is a cure for all the nation’s ills’. It is also used in the expression for good or ill, meaning ‘regardless of whether the effect is good or bad’, as in ‘He felt he wanted to remain part of the team, for good or ill’.