General term for illness or disease, typically excluding minor ailments like a common cold. Used in medical, everyday, and formal contexts.
He is hospitalized with a serious illness.
Hand washing is important for disease prevention.
Figurative use: a personal flaw, bad habit, or moral weakness likened to an illness. Often used in self-deprecating or critical remarks.
His chronic lateness is a bad habit of his.
Gambling might be an incurable weakness.
noun which may take the genitive case particle 'no'
crazy; insane; sick in the head
Colloquial, often used in phrases like 病気じゃない？ to suggest someone is mentally unstable or acting irrationally. Can be light-hearted or derogatory depending on context.
Going for a run at this hour? Are you crazy?
That idea seems nothing short of insane.
The doctor cured his illness.
Shopping that much all the time—that's just crazy.
After taking the medicine, the illness went away.
He missed school because he was sick.
My grandfather passed away from an illness.