Meaning of “illness” - Learner’s Dictionary

illness

noun uk us /ˈɪlnəs/
DISEASE [ C ]

B1 a disease of the body or mind:

a serious/terminal illness
He died at the age of 83 after a long illness.
BEING ILL [ U ]

B2 the state of being ill:

Unfortunately I couldn't go because of illness.

(Definition of “illness” from the Cambridge Learner’s Dictionary © Cambridge University Press)