1. To express great amusement or mirth: roar. Informal :break up. Slang :howl. SeeLAUGHTER. 2. To express amusement, mirth, or scorn by smiling and emitting loud, inarticulate sounds: cachinnate, cackle, laugh. Informal :heehaw. Idioms: die laughing, laugh one's head off, roll in the aisles, split one's sides. SeeLAUGHTER, SOUNDS.