The Collaborative International Dictionary of English v.0.48:

Knight \Knight\, n. [OE. knight, cniht, knight, soldier, AS.
   cniht, cneoht, a boy, youth, attendant, military follower;
   akin to D. & G. knecht servant; perh. akin to E. kin.]
   1. A young servant or follower; a military attendant. [Obs.]
      [1913 Webster]

   2.
      (a) In feudal times, a man-at-arms serving on horseback
          and admitted to a certain military rank with special
          ceremonies, including an oath to protect the
          distressed, maintain the right, and live a stainless
          life.
      (b) One on whom knighthood, a dignity next below that of
          baronet, is conferred by the sovereign, entitling him
          to be addressed as Sir; as, Sir John. [Eng.] Hence:
      (c) A champion; a partisan; a lover. "Give this ring to my
          true knight." Shak "In all your quarrels will I be
          your knight." --Tennyson.
          [1913 Webster]

                Knights, by their oaths, should right poor
                ladies' harms.                    --Shak.
          [1913 Webster]

   Note: Formerly, when a knight's name was not known, it was
         customary to address him as Sir Knight. The rank of a
         knight is not hereditary.
         [1913 Webster]

   3. A piece used in the game of chess, usually bearing a
      horse's head.
      [1913 Webster]

   4. A playing card bearing the figure of a knight; the knave
      or jack. [Obs.]
      [1913 Webster]

   Carpet knight. See under Carpet.

   Knight of industry. See Chevalier d'industrie, under
      Chevalier.

   Knight of Malta, Knight of Rhodes, Knight of St. John of
   Jerusalem. See Hospitaler.

   Knight of the post, one who gained his living by giving
      false evidence on trials, or false bail; hence, a sharper
      in general. --Nares. "A knight of the post, . . . quoth
      he, for so I am termed; a fellow that will swear you
      anything for twelve pence." --Nash.

   Knight of the shire, in England, one of the representatives
      of a county in Parliament, in distinction from the
      representatives of cities and boroughs.

   Knights commanders, Knights grand cross, different
      classes of the Order of the Bath. See under Bath, and
      Companion.

   Knights of labor, a secret organization whose professed
      purpose is to secure and maintain the rights of workingmen
      as respects their relations to their employers. [U. S.]

   Knights of Pythias, a secret order, founded in Washington,
      D. C., in 1864, for social and charitable purposes.

   Knights of the Round Table, knights belonging to an order
      which, according to the legendary accounts, was instituted
      by the mythical King Arthur. They derived their common
      title from the table around which they sat on certain
      solemn days. --Brande & C.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Knight \Knight\, v. t. [imp. & p. p. Knighted; p. pr. & vb. n.
   Knighting.]
   To dub or create (one) a knight; -- done in England by the
   sovereign only, who taps the kneeling candidate with a sword,
   saying: Rise, Sir ---.
   [1913 Webster]

         A soldier, by the honor-giving hand
         Of C[oe]ur-de-Lion knighted in the field. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

knight
    n 1: originally a person of noble birth trained to arms and
         chivalry; today in Great Britain a person honored by the
         sovereign for personal merit
    2: a chessman shaped to resemble the head of a horse; can move
       two squares horizontally and one vertically (or vice versa)
       [syn: knight, horse]
    v 1: raise (someone) to knighthood; "The Beatles were knighted"
         [syn: knight, dub]

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "knight":
   Bayard, Don Quixote, Gawain, Lancelot, Ritter, Sidney, Sir Galahad,
   advance, aggrandize, bachelor, banneret, baronet, battler,
   belligerent, belted knight, bickerer, bishop, blade, bravo,
   brawler, broncobuster, buckaroo, bully, bullyboy, caballero,
   castle, cavalier, cavalryman, chessman, chevalier, circus rider,
   combatant, companion, competitor, contender, contestant, cowboy,
   cowgirl, cowpuncher, disputant, duelist, elevate, enforcer,
   ennoble, equestrian, equestrienne, exalt, fencer, feuder, fighter,
   fighting cock, foilsman, gallant, gamecock, gaucho, gladiator,
   goon, gorilla, graduate, hatchet man, hood, hoodlum, hooligan,
   horse soldier, horseback rider, horsebacker, horseman, horsewoman,
   jockey, jouster, kick upstairs, king, knight bachelor,
   knight banneret, knight baronet, knight-errant, man, militant,
   mounted policeman, pass, pawn, piece, plug-ugly, postboy,
   postilion, prefer, promote, puncher, quarreler, queen, raise,
   rider, rioter, rival, rook, rough, roughrider, rowdy, ruffian,
   sabreur, scrapper, scuffler, squabbler, steeplechaser, strong arm,
   strong-arm man, strong-armer, struggler, swashbuckler, sword,
   swordplayer, swordsman, thug, tilter, tough, trick rider, tussler,
   up, upgrade, vaquero, wrangler



The Devil's Dictionary (1881-1906):

KNIGHT, n.

    Once a warrior gentle of birth,
    Then a person of civic worth,
    Now a fellow to move our mirth.
    Warrior, person, and fellow -- no more:
    We must knight our dogs to get any lower.
    Brave Knights Kennelers then shall be,
    Noble Knights of the Golden Flea,
    Knights of the Order of St. Steboy,
    Knights of St. Gorge and Sir Knights Jawy.
    God speed the day when this knighting fad
    Shall go to the dogs and the dogs go mad.