ill

When used as an adjective meaning 'sick', "ill" is more common in British English, whereas American English speakers typically prefer the word "sick". As an adverb, it is often used in specific set phrases like "speak ill of someone," meaning to criticize them. It is not usually used as a general replacement for the word "badly" (for example, you would say "he plays guitar badly", not "he plays guitar ill"). When used as a noun, it almost always refers to a wide social problem or a misfortune rather than a personal physical illness.