To cluck means to make the short, sharp sound that a chicken makes, a sort of “buk-buk-buk” noise that chickens use to communicate with each other. A hen clucks to call her chicks, to show contentment while pecking for food, or sometimes to announce she's laid an egg.

The word also describes the similar sound people make with their tongue against the roof of their mouth, often to express disapproval or sympathy. You might cluck your tongue when you see someone make a foolish mistake, or when you hear disappointing news. A grandmother might cluck sympathetically while examining a child's scraped knee.

When someone clucks over something, they're fussing about it in a concerned, sometimes slightly annoying way. A teacher might cluck over students who forgot their homework, making disapproving sounds while shaking her head. Parents sometimes cluck over their children's messy rooms or uncombed hair, expressing mild frustration with that distinctive clicking sound.