[1] : The Collaborative International Dictionary of English v.0.48

knock \knock\ no^k, v. i. imp.  p. p. knocked no^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.
      1913 webster

   2. to strike or beat with something hard or heavy; to rap;
      as, to knock with a club; to knock on the door.
      1913 webster

            for harbor at a thousand doors they knocked.
                                                  --dryden.
      1913 webster

            seek, and ye shall find; knock, and it shall be
            opened unto you.                      --matt. vii.
                                                  7.
      1913 webster

   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.
      1913 webster
see also:
knocked knocking knack to knock about to knock up to knock off 
to knock under 

Knock >> K Words
Knock, definition of term: Knock
knock_pag1.html

Go Under >> G Words
Go Under, definition of term: Go Under
go+under_pag1.html