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.
      [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]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            When heroes knock their knotty heads together.
                                                  --Rowe.
      [1913 Webster]

   2. To strike for admittance; to rap upon, as a door.
      [1913 Webster]

            Master, knock the door hard.          --Shak.
      [1913 Webster]

   3. To impress strongly or forcibly; to astonish; to move to
      admiration or applause. [Slang, Eng.]
      [Webster 1913 Suppl.]

   4. To criticise; to find fault with; to disparage. "Don't
      knock it if you haven't tried it."
      [PJC]

   To knock in the head, or To knock 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.
      (d) To make pregnant. Often used in passive, "she got
          knocked up". [vulgar]

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:

backfire \backfire\, back fire \back fire\
   1. A fire started ahead of a forest or prairie fire to burn
      only against the wind, so that when the two fires meet
      both must go out for lack of fuel.
      [Webster 1913 Suppl.]

   2.
      (a) A premature explosion in the cylinder of a gas or oil
          engine during the exhaust or the compression stroke,
          tending to drive the piston in a direction reverse to
          that in which it should travel; also called a knock
          or ping.
      (b) an explosion in the exhaust passages of an internal
          combustion engine.
          [Webster 1913 Suppl. +PJC] Backfire

WordNet (r) 3.0 (2006):

knock
    n 1: the sound of knocking (as on a door or in an engine or
         bearing); "the knocking grew louder" [syn: knock,
         knocking]
    2: negative criticism [syn: knock, 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:
       knock, 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: knock, belt, rap, whack, whang]
    v 1: deliver a sharp blow or push :"He knocked the glass clear
         across the room" [syn: knock, 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, knock]
    4: make light, repeated taps on a surface; "he was tapping his
       fingers on the table impatiently" [syn: tap, rap,
       knock, 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,
       knock]
    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: knock, criticize,
       criticise, pick apart] [ant: praise]

Moby Thesaurus II by Grady Ward, 1.0:

271 Moby Thesaurus words for "knock":
   KO, abuse, adverse criticism, animadversion, arouse, aspersion,
   associate with, astonish, astound, awaken, bad notices, bad press,
   bang, bang into, bash, baste, bat, batter, beat, beat up, beating,
   belt, bewilder, biff, blame, blow, bob, bonk, bop, bowl over,
   buffet, bump, bump into, burst, bust, cannon, captiousness, carom,
   carom into, carp at, carping, cavil, caviling, censoriousness,
   censure, chop, clap, clash, clip, clobber, clock out, close down,
   clout, clump, coldcock, collide, come into collision, complete,
   concuss, condemn, condemnation, confront each other, conk,
   consort with, copy, crack, crack up, crash, crash into, criticism,
   criticize, crump, crunch, cuff, cut, cut down, dash, dash into,
   daze, deal, deal a blow, debate, deck, demolish, denounce,
   denunciate, deprecate, destroy, dig, dint, discuss, disparage,
   drub, drubbing, drumming, encounter, exception, fall foul of,
   faultfinding, fell, fetch, fetch a blow, finish, flail, flak, flap,
   flatten, floor, flop, foul, fusillade, gad about, get with child,
   go home, hairsplitting, hammer, hammering, hit, hit a clip,
   hit against, home thrust, hostile criticism, hurt, hurtle,
   hypercriticalness, hypercriticism, imitate, impinge, impregnate,
   improvise, imputation, insult, jab, kayo, kill, knock about,
   knock against, knock around, knock cold, knock down, knock off,
   knock out, knock over, knock together, knock unconscious, knock up,
   lambaste, larrup, lay in ruins, left, let have it, level, lick,
   lift, lock up, maltreat, manhandle, maul, meet, mistreat, nagging,
   nick, niggle, niggling, nit, nit-picking, obloquy, overcome,
   overcriticalness, overwhelm, pan, paste, patter, pelt, percuss,
   pestering, pettifogging, pilfer, pinch, plunk, poke, polish off,
   pommel, pound, pounding, priggishness, prostrate, pull down,
   pulverize, pummel, punch, put down, put together, quibble,
   quibbling, quit, ramble, rap, raze, reflection, report, reprehend,
   reproachfulness, reprobate, right, roam, rob, rove, run down,
   run into, sideswipe, skin, slam, slam into, slap, slat,
   sledgehammer, slog, slug, slur, smack, smack into, smash,
   smash into, smash up, smite, snap, snipe at, soak, sock, spank,
   splat, stagger, steal, stricture, strike, strike against,
   strike at, stroke, stun, swap, swat, swing, swipe,
   taking exception, talk over, tap, tattoo, terminate, thieve,
   thrash, thresh, throw down, thump, thwack, travel, trichoschistism,
   trounce, tunk, wake up, wallop, wander, whack, wham, whap, whip,
   whomp, whop, wipe, wreck, yerk



Easton's 1897 Bible Dictionary:

Knock
   "Though Orientals are very jealous of their privacy, they never
   knock when about to enter your room, but walk in without warning
   or ceremony. It is nearly impossible to teach an Arab servant to
   knock at your door. They give warning at the outer gate either
   by calling or knocking. To stand and call is a very common and
   respectful mode. Thus Moses commanded the holder of a pledge to
   stand without and call to the owner to come forth (Deut. 24:10).
   This was to avoid the violent intrusion of cruel creditors.
   Peter stood knocking at the outer door (Acts 12:13, 16), and the
   three men sent to Joppa by Cornelius made inquiry and 'stood
   before the gate' (10:17, 18). The idea is that the guard over
   your privacy is to be placed at the entrance."

     Knocking is used as a sign of importunity (Matt. 7:7, 8; Luke
   13:25), and of the coming of Christ (Luke 12:36; Rev. 3:20).