The Collaborative International Dictionary of English v.0.48:

Knock \Knock\ (n[o^]k), v. i. [imp. & p. p. Knocked (n[o^]kt);
   p. pr. & vb. n. Knocking.] [OE. knoken, AS. cnocian,
   cnucian; prob. of imitative origin; cf. Sw. knacka. Cf.
   Knack.]
   1. To drive or be driven against something; to strike against
      something; to clash; as, one heavy body knocks against
      another. --Bacon.
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   2. To strike or beat with something hard or heavy; to rap;
      as, to knock with a club; to knock on the door.
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            For harbor at a thousand doors they knocked.
                                                  --Dryden.
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            Seek, and ye shall find; knock, and it shall be
            opened unto you.                      --Matt. vii.
                                                  7.
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   3. To practice evil speaking or fault-finding; to criticize
      habitually or captiously. [Slang, U. S.]
      [Webster 1913 Suppl.]

   To knock about, to go about, taking knocks or rough usage;
      to wander about; to saunter. [Colloq.] "Knocking about
      town." --W. Irving.

   To knock up, to fail of strength; to become wearied or worn
      out, as with labor; to give out. "The horses were
      beginning to knock up under the fatigue of such severe
      service." --De Quincey.

   To knock off, to cease, as from work; to desist.

   To knock under, to yield; to submit; to acknowledge one's
      self conquered; -- an expression probably borrowed from
      the practice of knocking under the table with the
      knuckles, when conquered. "Colonel Esmond knocked under to
      his fate." --Thackeray.
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