Knock"er (?), 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.

Shut, shut the door, good John ! fatigued, I said;
Tie up the knocker; say I'm sick, I'm dead.
Pope.

© [Webster 1913]

Knock"er (?), n.

1.

A person strikingly handsome, beautiful, or fine; one who wins admiration; a "stunner." [Slang.]

2.

A species of large cockroach, esp. Blabera gigantea, of semitropical America, which is able to produce a loud knocking sound.

© [Webster 1913]

Knocker (definition)