knock·er /ˈnɑkɚ/
 敲擊者,敲門者,門環
 knock·er n.
 1. 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.
 2. A person strikingly handsome, beautiful, or fine; one who wins admiration; a “stunner.” [Slang.]
 3.  A species of large cockroach, especially Blabera gigantea, of semitropical America, which is able to produce a loud knocking sound.
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 knocker
      n 1: (Yiddish) a big shot who knows it and acts that way; a
           boastful immoderate person
      2: a person who knocks (as seeking to gain admittance); "open
         the door and see who the knocker is"
      3: one who disparages or belittles the worth of something [syn:
          detractor, disparager, depreciator]
      4: either of two soft fleshy milk-secreting glandular organs on
         the chest of a woman [syn: breast, bosom, boob, tit,
          titty]
      5: a device (usually metal and ornamental) attached by a hinge
         to a door [syn: doorknocker, rapper]