unwellun‧well /ʌnˈwel/ ●○○ adjective [not before noun] 
Examples
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.
ExamplesEXAMPLES FROM OTHER DICTIONARIES
Thesaurus- Mrs Hedges is unwell today, so her class will be taken by Mr Collier.
- Tom had been unwell for some time but had refused to see a doctor.
- By lunchtime she was distinctly unwell and the school nurse told her she had a temperature and sent her home.
- It is best to make a firm rule not to fly if you are feeling unwell or unenthusiastic.
- Loi felt very unwell, and Joe was trying to treat the infection with a different type of antibiotic.
- Ruth had decided to say she'd been unwell, and had been given a few days off to recover her strength.
- When we feel unwell in some way or another we do not always recognize stress as the culprit.
- Yesterday he was rowing with the boat race squad on this stretch of Thames at Wallingford when he complained he felt unwell.
THESAURUS► ill
formal ill, especially for a short time: [not before noun] especially British English suffering from a disease or not feeling well: · Her mother is seriously ill in hospital.· I woke up feeling really ill.
► sick especially American English ill: · She’s been sick with the flu.· a sick child· Dan got sick on vacation.
► not very well [not before noun] ill, but not seriously ill: · Sarah’s not very well – she has a throat infection.
► unwell [not before noun] formal ill: · The singer had been unwell for some time.· Symptoms include fever, aching muscles, and feeling generally unwell.
► poorly [not before noun] BrE spoken ill: · Your grandmother’s been very poorly lately.
► in a bad way [not before noun] very ill because of a serious injury or disease: · You’d better call an ambulance – she looks like she’s in a bad way.
► be off sick British English, be out sick American English to be not at work because of an illness: · Two teachers were off sick yesterday.
Longman Language Activatorill► ill especially British suffering from bad health or not feeling well: · Mel was so ill that she had to stay in bed for a month.seriously ill (=very ill): · Apparently Don's wife is seriously ill, and they think it might be cancer.critically ill (=extremely ill): · The baby caught a virus and became critically ill.terminally ill (=so ill that you are going to die): · psychological support for terminally ill patientsmentally ill (=suffering from a mental illness): · Mentally ill patients have the same rights as anyone else.lie ill (=be ill in bed): · All that week, Catherine lay ill, drifting in and out of consciousness.
► sick especially American ill: · Where's Mary today? I hope she's not sick again.· Sheila spent months looking after her sick mother.be off sick (=not at work or school because of illness): · Gary phoned to say that he's off sick today.be off work sick/be in bed sick: · I'm sorry I didn't reply to your e-mail. I was in bed sick for a couple of days.sick with the flu/a virus etc (=ill as a result of flu etc): · Grant Hill played despite being sick with the flu for the past ten days.be sick with worry/fear/exhaustion etc (=so worried etc that you feel sick): · We were dirty, hungry, cold and sick with exhaustion.
► be not (very) well especially spoken to be ill, but not seriously ill: · Sarah's not very well - she's got a throat infection.· Jed's Mum says he's not well, so he's staying at home today.
► unwell formal ill: · Mrs Hedges is unwell today, so her class will be taken by Mr Collier.· Tom had been unwell for some time but had refused to see a doctor.
► poorly British informal ill: · Dad was always out, Mum was often poorly, and I had to look after the rest of the kids.· "I'm afraid your grandmother's very poorly," the nurse on duty said.
► be in a bad way informal to be very ill, especially as a result of a serious injury or disease: · You'd better get an ambulance - she's in a pretty bad way.· Martin came back from Africa with malaria, and he was in a pretty bad way for months.
► look like death warmed up British /death warmed over American spoken to look ill and pale, especially because you did not get enough sleep or are suffering for the effects of too much alcohol: · Kate didn't sleep a wink last night. She looks like death warmed up.· Boy, you look like death warmed over this morning!
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.