noun

• A device, usually hinged with a striking plate, used for knocking on a door.
• A person who knocks.
• A critic; one who disparages.
• (informal, derogatory) A person who knocks (denigrates) something.
• (slang, usually in the plural) A woman's breast.
• (especially Cardigan, in South Wales, archaic) A dwarf, goblin, or sprite imagined to dwell in mines and to indicate the presence of ore by knocking.
• (pinball) A mechanical device in a pinball table that produces a loud percussive noise.
• (dated, slang) A person who is strikingly handsome or otherwise admirable; a stunner.
• A large cockroach, especially Blaberus giganteus, of semitropical America, which is able to produce a loud knocking sound.
• (geology) A large, boulder-shaped outcrop of bedrock in an otherwise low-lying landscape, chiefly associated with a mélange.
• (slang) One who defaults on payment of a wager.
• A surname.