fromEnglish Grammar Today
Illandsickareboth adjectives that mean ‘not in good health’. We use bothillandsickafter a verb such asbe, become, feel, lookorseem:
I wasillfor a time last year, but I’m fine now.
Nancy looksill. I wonder what’s wrong with her.
I feltsickand had to go home at lunchtime.
We can usesickbefore a noun but we don’t normally useillbefore a noun:
She’s been looking after asickchild this week, so she’s not at work.
Not: …an ill child…
Note thatto be sickmeans ‘to vomit’ in British English. In American Englishit means more generally ‘to be unwell’.