From Longman Dictionary of Contemporary Englishunwellun‧well /ʌnˈwel/ ●○○ adjective [not before noun] formalILL ill, especially for a short time She had been feeling unwell.► see thesaurus at illRegisterIn everyday English, people usually say that someone is not well rather than unwell:He didn’t come to school because he wasn’t well.
Examples from the Corpus
unwell• Yesterday he was rowing with the boat race squad on this stretch of Thames at Wallingford when he complained he felt unwell.• Ruth had decided to say she'd been unwell, and had been given a few days off to recover her strength.• Loi felt very unwell, and Joe was trying to treat the infection with a different type of antibiotic.• By lunchtime she was distinctly unwell and the school nurse told her she had a temperature and sent her home.• Tom had been unwell for some time but had refused to see a doctor.• When we feel unwell in some way or another we do not always recognize stress as the culprit.• It is best to make a firm rule not to fly if you are feeling unwell or unenthusiastic.• Mrs Hedges is unwell today, so her class will be taken by Mr Collier. 