Source : Webster's Revised Unabridged Dictionary (1913)

Knock \Knock\, v. i. [imp. & p. p. {Knocked}; 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.

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

            For harbor at a thousand doors they knocked.
                                                  --Dryden.

            Seek, and ye shall find; knock, and it shall be
            opened unto you.                      --Matt. vii.
                                                  7.

   {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.

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

   2. A stroke, as on a door for admittance; a rap. `` A knock
      at the door.'' --Longfellow.

            A loud cry or some great knock.       --Holland.

   {Knock off}, a device in a knitting machine to remove loops
      from the needles.

Knock \Knock\ (n[o^]k), v. t.
   1. To strike with something hard or heavy; to move by
      striking; to drive (a thing) against something; as, to
      knock a ball with a bat; to knock the head against a post;
      to knock a lamp off the table.

            When heroes knock their knotty heads together.
                                                  --Rowe.

   2. To strike for admittance; to rap upon, as a door.

            Master, knock the door hard.          --Shak.

   {To knock down}.
      (a) To strike down; to fell; to prostrate by a blow or by
          blows; as, to knock down an assailant.
      (b) To assign to a bidder at an auction, by a blow or
          knock; to knock off.

   {To knock in the head}, or {on the head}, to stun or kill by
      a blow upon the head; hence, to put am end to; to defeat,
      as a scheme or project; to frustrate; to quash. [Colloq.]
      -- {To knock off}.
      (a) To force off by a blow or by beating.
      (b) To assign to a bidder at an auction, by a blow on the
          counter.
      (c) To leave off (work, etc.). [Colloq.] -- {To knock
   out}, to force out by a blow or by blows; as, to knock out
      the brains.

   {To knock up}.
      (a) To arouse by knocking.
      (b) To beat or tire out; to fatigue till unable to do
          more; as, the men were entirely knocked up. [Colloq.]
          ``The day being exceedingly hot, the want of food had
          knocked up my followers.'' --Petherick.
      (c) (Bookbinding) To make even at the edges, or to shape
          into book form, as printed sheets.

Knock \Knock\, v. i.
   To practice evil speaking or fault-finding; to criticize
   habitually or captiously. [Vulgar Slang, U. S.]

Knock \Knock\, v. t.
   To impress strongly or forcibly; to astonish; to move to
   admiration or applause. [Slang, Eng.]

Source : WordNet®

knock
     n 1: the sound of knocking (as on a door or in an engine or
          bearing); "the knocking grew louder" [syn: {knocking}]
     2: negative criticism [syn: {roast}]
     3: a vigorous blow; "the sudden knock floored him"; "he took a
        bash right in his face"; "he got a bang on the head" [syn:
         {bash}, {bang}, {smash}, {belt}]
     4: a bad experience; "the school of hard knocks"
     5: the act of hitting vigorously; "he gave the table a whack"
        [syn: {belt}, {rap}, {whack}, {whang}]

knock
     v 1: deliver a sharp blow or push :"He knocked the glass clear
          across the room" [syn: {strike hard}]
     2: rap with the knuckles; "knock on the door"
     3: knock against with force or violence; "My car bumped into
        the tree" [syn: {bump}]
     4: make light, repeated taps on a surface; "he was tapping his
        fingers on the table impatiently" [syn: {tap}, {rap}, {pink}]
     5: sound like a car engine that is firing too early; "the car
        pinged when I put in low-octane gasoline"; "The car pinked
        when the ignition was too far retarded" [syn: {pink}, {ping}]
     6: find fault with; express criticism of; point out real or
        perceived flaws; "The paper criticized the new movie";
        "Don't knock the food--it's free" [syn: {criticize}, {criticise},
         {pick apart}] [ant: {praise}]