The Collaborative International Dictionary of English v.0.48:

Knock \Knock\, n.
   1. A blow; a stroke with something hard or heavy; a jar.
      [1913 Webster]

   2. A stroke, as on a door for admittance; a rap. " A knock at
      the door." --Longfellow.
      [1913 Webster]

            A loud cry or some great knock.       --Holland.
      [1913 Webster]

   Knock off, See knock off in the vocabulary.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

knock off \knock off\, n.
   a device in a knitting machine to remove loops from the
   needles.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

knock off \knock off\, v. i. & t.
   1. to quit (working).
      [PJC]

   2. to accomplish; -- frequently used when the task is
      accomplished rapidly.
      [PJC]

   3. to kill; to defeat (opponents). [Colloq.]
      [PJC]

   4. to discount, to deduct (a sum from a price).
      [PJC]

   5. to rob.

   Syn: knock over.
        [PJC]

   6. to make a knockoff of; to copy or imitate, usually without
      permission or admission of copying. --[MW10]
      [PJC]

WordNet (r) 3.0 (2006):

knock off
    v 1: get rid of (someone who may be a threat) by killing; "The
         mafia liquidated the informer"; "the double agent was
         neutralized" [syn: neutralize, neutralise, liquidate,
         waste, knock off, do in]
    2: cut the price of [syn: shave, knock off]
    3: take by theft; "Someone snitched my wallet!" [syn: hook,
       snitch, thieve, cop, knock off, glom]
    4: write quickly; "She dashed off a note to her husband saying
       she would not be home for supper"; "He scratched off a thank-
       you note to the hostess" [syn: dash off, scratch off,
       knock off, toss off, fling off]
    5: stop pursuing or acting; "drop a lawsuit"; "knock it off!"
       [syn: drop, knock off]