The Collaborative International Dictionary of English v.0.48:

Giant \Gi"ant\, a.
   Like a giant; extraordinary in size, strength, or power; as,
   giant brothers; a giant son.
   [1913 Webster]

   Giant cell. (Anat.) See Myeloplax.

   Giant clam (Zool.), a bivalve shell of the genus
      Tridacna, esp. T. gigas, which sometimes weighs 500
      pounds. The shells are sometimes used in churches to
      contain holy water.

   Giant heron (Zool.), a very large African heron (Ardeomega
      goliath). It is the largest heron known.

   Giant kettle, a pothole of very large dimensions, as found
      in Norway in connection with glaciers. See Pothole.

   Giant powder. See Nitroglycerin.

   Giant puffball (Bot.), a fungus (Lycoperdon giganteum),
      edible when young, and when dried used for stanching
      wounds.

   Giant salamander (Zool.), a very large aquatic salamander
      (Megalobatrachus maximus), found in Japan. It is the
      largest of living Amphibia, becoming a yard long.

   Giant squid (Zool.), one of several species of very large
      squids, belonging to Architeuthis and allied genera.
      Some are over forty feet long.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Giant \Gi"ant\, n. [OE. giant, geant, geaunt, OF. jaiant, geant,
   F. g['e]ant, L. gigas, fr. Gr. ?, ?, from the root of E.
   gender, genesis. See Gender, and cf. Gigantic.]
   [1913 Webster]
   1. A man of extraordinari bulk and stature.
      [1913 Webster]

            Giants of mighty bone and bold emprise. --Milton.
      [1913 Webster]

   2. A person of extraordinary strength or powers, bodily or
      intellectual.
      [1913 Webster]

   3. Any animal, plant, or thing, of extraordinary size or
      power.
      [1913 Webster]

   Giant's Causeway, a vast collection of basaltic pillars, in
      the county of Antrim on the northern coast of Ireland.
      [1913 Webster]

WordNet (r) 3.0 (2006):

giant
    adj 1: of great mass; huge and bulky; "a jumbo jet"; "jumbo
           shrimp" [syn: elephantine, gargantuan, giant,
           jumbo]
    n 1: any creature of exceptional size
    2: a person of exceptional importance and reputation [syn:
       colossus, behemoth, giant, heavyweight, titan]
    3: an unusually large enterprise; "Walton built a retail giant"
    4: a very large person; impressive in size or qualities [syn:
       giant, hulk, heavyweight, whale]
    5: someone or something that is abnormally large and powerful
       [syn: giant, goliath, behemoth, monster, colossus]
    6: an imaginary figure of superhuman size and strength; appears
       in folklore and fairy tales
    7: a very bright star of large diameter and low density
       (relative to the Sun) [syn: giant star, giant]

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "giant":
   Amazon, Antaeus, Atlantean, Atlas, Briareus, Brobdingnagian,
   Charles Atlas, Cyclopean, Cyclops, Gargantua, Gargantuan, Goliath,
   Herculean, Hercules, Homeric, Orion, Polyphemus, Samson, Superman,
   Tarzan, Titan, abysmal, amazon, astronomic, bean pole, behemoth,
   bully, bullyboy, colossal, colossus, cyclopean, cyclops,
   elephantine, enormous, epic, gangling, gangly, gargantuan,
   giantlike, gigantic, gorilla, grenadier, gross, heroic, huge,
   hulking, immense, infinite, jumbo, lank, lanky, leggy, lengthy,
   leviathan, long, long-legged, longlegs, longshanks, mammoth,
   mighty, monster, monstrous, monumental, mountainous, muscle man,
   ogre, powerhouse, prodigious, profound, rangy, seven-footer,
   stalwart, statuesque, strong man, strong-arm man, stupendous,
   superhuman, tall, the mighty, the strong, titan, titanic, tough,
   tough guy, tower of strength, towering, tremendous, vast, whale