The Collaborative International Dictionary of English v.0.48:

Cockatrice \Cock"a*trice\ (-tr[imac]s; 277), n. [OF. cocatrice
   crocodile, F. cocatrix, cocatrice. The word is a corruption
   from the same source as E. crocodile, but was confused with
   cock the bird, F. coq, whence arose the fable that the animal
   was produced from a cock's egg. See Crocodile.]
   [1913 Webster]
   1. A fabulous serpent whose breath and look were said to be
      fatal. See Basilisk.
      [1913 Webster]

            That bare vowel, I, shall poison more
            Than the death-darting eye of cockatrice. --Shak.
      [1913 Webster]

   2. (Her.) A representation of this serpent. It has the head,
      wings, and legs of a bird, and tail of a serpent.
      [1913 Webster]

   3. (Script.) A venomous serpent which which cannot now be
      identified.
      [1913 Webster]

            The weaned child shall put his hand on the
            cockatrice's

   Note: [Rev. Ver. basilisk's] den.              --Is. xi. 8.
   [1913 Webster]

   4. Any venomous or deadly thing.
      [1913 Webster]

            This little cockatrice of a king.     --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cockatrice
    n 1: monster hatched by a reptile from a cock's egg; able to
         kill with a glance

Moby Thesaurus II by Grady Ward, 1.0:

130 Moby Thesaurus words for "cockatrice":
   Benedict Arnold, Brutus, Judas, Judas Iscariot, Quisling,
   achievement, alerion, animal charge, annulet, archtraitor, argent,
   armorial bearings, armory, arms, azure, bandeau, bar, bar sinister,
   baton, bearings, bend, bend sinister, betrayer, billet, blazon,
   blazonry, bordure, broad arrow, cadency mark, canton, chaplet,
   charge, chevron, chief, coat of arms, conniver, conspirator,
   conspirer, coronet, crescent, crest, cross, cross moline, crown,
   device, difference, differencing, double agent, double-crosser,
   double-dealer, eagle, ermine, ermines, erminites, erminois,
   escutcheon, falcon, fess, fess point, field, file, flanch,
   fleur-de-lis, fret, fur, fusil, garland, griffin, gules, gyron,
   hatchment, helmet, heraldic device, honor point, impalement,
   impaling, inescutcheon, informer, intrigant, intriguer, label,
   lion, lozenge, machinator, mantling, marshaling, martlet, mascle,
   metal, motto, mullet, nombril point, octofoil, or, ordinary, orle,
   pale, paly, pean, pheon, plotter, purpure, quarter, quartering,
   quisling, rat, rose, sable, saltire, schemer, scutcheon, serpent,
   shield, snake, spread eagle, subordinary, tenne, timeserver,
   tincture, torse, traitor, treasonist, tressure, trimmer, turncoat,
   unicorn, vair, vert, wreath, yale



Easton's 1897 Bible Dictionary:

Cockatrice
   the mediaeval name (a corruption of "crocodile") of a fabulous
   serpent supposed to be produced from a cock's egg. It is
   generally supposed to denote the cerastes, or "horned viper," a
   very poisonous serpent about a foot long. Others think it to be
   the yellow viper (Daboia xanthina), one of the most dangerous
   vipers, from its size and its nocturnal habits (Isa. 11:8;
   14:29; 59:5; Jer. 8:17; in all which the Revised Version renders
   the Hebrew _tziph'oni_ by "basilisk"). In Prov. 23:32 the Hebrew
   _tzeph'a_ is rendered both in the Authorized Version and the
   Revised Version by "adder;" margin of Revised Version
   "basilisk," and of Authorized Version "cockatrice."