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