noun, noun which may take the genitive case particle 'no'
serious illness; severe disease
Refers to a life-threatening or very grave medical condition. Often used in formal or medical contexts, and can modify nouns with の.
My grandfather is hospitalized with a serious illness.
A new treatment has been developed for seriously ill patients.
My grandfather came down with a serious illness and was hospitalized.
He once suffered from a serious illness when he was young.