What is the meaning of Knocker?

A device, usually hinged with a striking plate, used for knocking on a door.

A person who knocks.

A critic; one who disparages.

A person who knocks (denigrates) something.

A person's breast, especially if large.

A dwarf, goblin, or sprite imagined to dwell in mines and to indicate the presence of ore by knocking.

A mechanical device in a pinball table that produces a loud percussive noise.

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.

A large, boulder-shaped outcrop of bedrock in an otherwise low-lying landscape, chiefly associated with a mélange.

One who defaults on payment of a wager.

A gun.

An undercover policeman.

Source: wiktionary.org