to be concerned about; to be interested in; to be bothered by; to have a problem with

(idiomatic) Alternative form of 気が気でない

(idiomatic) very anxious, very worried, feeling uneasy; can't help but be worried

(idiomatic) Alternative form of 気が気でない

(mathematics) quod erat demonstrandum (that which was to be proved)

(Internet slang) a dead fad; out of fashion; no longer trendy

a sign

(idiomatic) to cause concern, to be worrisome, to be on one's mind / to be interested, to be curious

(idiomatic) to care about something, to pay undue attention to something, to mind something which is a negative nuance, to worry about something

plain negative imperative form of 気にする: never mind!; don't worry about it.