knocker

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A hinged fixture, such as a metal ring or bar, used for knocking on a door.
2. n. Vulgar Slang A woman's breasts.
3. n. A goblin or dwarf said to live under the earth and direct miners to ore by knocking.

Century Dictionary and Cyclopedia

1. n. One who knocks.
2. n. A spirit or goblin supposed to dwell in mines, and to indicate the presence of rich veins of ore by knocking.
3. n. A knob, bar, or ring of metal attached to an outer door, by knocking with which persons seeking admittance can attract the notice of the inmates. It is usually so held by a hinge that it can be lifted and allowed to fall against a metal plate or stud, giving a sharp blow. It has now generally given place to the door-bell.
4. n. In milling, a device attached to a flour-bolt to jar or shake it at intervals, in order to free the cloth from the flour.
5. n. One who keeps up a system of ‘knocking’ or persistent attack, with ulterior motives. See knock, v. i., 4.
6. n. A sort of pendant to a wig.

Wiktionary

1. n. A device, usually hinged with a striking plate, used for knocking on a door.
2. n. A person who knocks (denigrates) many things.
3. n. slang (usually in plural) A woman's breasts.
4. n. A dwarf, goblin, or sprite imagined to dwell in mines and to indicate the presence of ore by knocking particularly in Cardigan etc. in South Wales (18th..19th century).
5. n. pinball A mechanical device in a pinball table that produces a loud percussive noise.

GNU Webster's 1913

1. n. One who, or that which, knocks; specifically, an instrument, or kind of hammer, fastened to a door, to be used in seeking for admittance.
2. n. Slang. A person strikingly handsome, beautiful, or fine; one who wins admiration; a “stunner.”
3. n. A species of large cockroach, especially Blabera gigantea, of semitropical America, which is able to produce a loud knocking sound.
4. n. vulgar a woman's breast.

WordNet 3.0

1. n. a person who knocks (as seeking to gain admittance)
2. n. (Yiddish) a big shot who knows it and acts that way; a boastful immoderate person
3. n. either of two soft fleshy milk-secreting glandular organs on the chest of a woman
4. n. a device (usually metal and ornamental) attached by a hinge to a door
5. n. one who disparages or belittles the worth of something