The Collaborative International Dictionary of English v.0.48:

Gray \Gray\ (gr[=a]), a. [Compar. Grayer; superl. Grayest.]
   [OE. gray, grey, AS. gr[=ae]g, gr[=e]g; akin to D. graauw,
   OHG. gr[=a]o, G. grau, Dan. graa, Sw. gr[*a], Icel. gr[=a]r.]
   [Written also grey.]
   1. any color of neutral hue between white and black; white
      mixed with black, as the color of pepper and salt, or of
      ashes, or of hair whitened by age; sometimes, a dark mixed
      color; as, the soft gray eye of a dove.
      [1913 Webster]

            These gray and dun colors may be also produced by
            mixing whites and blacks.             --Sir I.
                                                  Newton.
      [1913 Webster]

   2. Gray-haired; gray-headed; of a gray color; hoary.
      [1913 Webster]

   3. Old; mature; as, gray experience. -- Ames.
      [1913 Webster]

   4. gloomy; dismal.
      [PJC]

   Gray antimony (Min.), stibnite.

   Gray buck (Zool.), the chickara.

   Gray cobalt (Min.), smaltite.

   Gray copper (Min.), tetrahedrite.

   Gray duck (Zool.), the gadwall; also applied to the female
      mallard.

   Gray falcon (Zool.) the peregrine falcon.

   Gray Friar. See Franciscan, and Friar.

   Gray hen (Zool.), the female of the blackcock or black
      grouse. See Heath grouse.

   Gray mill or Gray millet (Bot.), a name of several plants
      of the genus Lithospermum; gromwell.

   Gray mullet (Zool.) any one of the numerous species of the
      genus Mugil, or family Mugilid[ae], found both in the
      Old World and America; as the European species
      (Mugilid[ae] capito, and Mugilid[ae] auratus), the
      American striped mullet (Mugilid[ae] albula), and the
      white or silver mullet (Mugilid[ae] Braziliensis). See
      Mullet.

   Gray owl (Zool.), the European tawny or brown owl (Syrnium
      aluco). The great gray owl (Ulula cinerea) inhabits
      arctic America.

   Gray parrot (Zool.), an African parrot (Psittacus
      erithacus), very commonly domesticated, and noted for its
      aptness in learning to talk. Also called jako.

   Gray pike. (Zool.) See Sauger.

   Gray snapper (Zool.), a Florida fish; the sea lawyer. See
      Snapper.

   Gray snipe (Zool.), the dowitcher in winter plumage.

   Gray whale (Zool.), a rather large and swift whale of the
      northern Pacific (Eschrichtius robustus, formerly
      Rhachianectes glaucus), having short jaws and no dorsal
      fin. It grows to a length of 50 feet (someimes 60 feet).
      It was formerly taken in large numbers in the bays of
      California, and is now rare; -- called also grayback,
      devilfish, and hardhead. It lives up to 50 or 60 years
      and adults weigh from 20 to 40 tons.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Grey \Grey\, a.
   See Gray (the correct orthography).
   [1913 Webster]

WordNet (r) 3.0 (2006):

grey
    adj 1: of an achromatic color of any lightness intermediate
           between the extremes of white and black; "the little grey
           cells"; "gray flannel suit"; "a man with greyish hair"
           [syn: grey, gray, greyish, grayish]
    2: showing characteristics of age, especially having grey or
       white hair; "whose beard with age is hoar"-Coleridge; "nodded
       his hoary head" [syn: grey, gray, grey-haired, gray-
       haired, grey-headed, gray-headed, grizzly, hoar,
       hoary, white-haired]
    3: used to signify the Confederate forces in the American Civil
       War (who wore grey uniforms); "a stalwart grey figure" [syn:
       grey, gray]
    4: intermediate in character or position; "a grey area between
       clearly legal and strictly illegal" [syn: grey, gray]
    n 1: United States writer of western adventure novels
         (1875-1939) [syn: Grey, Zane Grey]
    2: Queen of England for nine days in 1553; she was quickly
       replaced by Mary Tudor and beheaded for treason (1537-1554)
       [syn: Grey, Lady Jane Grey]
    3: Englishman who as Prime Minister implemented social reforms
       including the abolition of slavery throughout the British
       Empire (1764-1845) [syn: Grey, Charles Grey, Second Earl
       Grey]
    4: any organization or party whose uniforms or badges are grey;
       "the Confederate army was a vast grey" [syn: grey, gray]
    5: a neutral achromatic color midway between white and black
       [syn: gray, grayness, grey, greyness]
    6: clothing that is a grey color; "he was dressed in grey" [syn:
       grey, gray]
    7: horse of a light gray or whitish color [syn: grey, gray]
    v 1: make grey; "The painter decided to grey the sky" [syn:
         grey, gray]
    2: turn grey; "Her hair began to grey" [syn: grey, gray]

Moby Thesaurus II by Grady Ward, 1.0:

203 Moby Thesaurus words for "grey":
   Quaker-colored, achromatic, achromic, acier, advanced,
   advanced in life, advanced in years, aged, along in years, ancient,
   anemic, ashen, ashy, bay, bayard, black, bleak, bled white,
   bloodless, boring, buckskin, cadaverous, calico pony, canescence,
   canescent, cheerless, chestnut, chloranemic, cinereous, cinerous,
   cloudy, colorless, dapple, dapple-gray, dappled, dappled-gray,
   dark, dead, deadly pale, deathly pale, depressing, dim, dimmed,
   dingy, discolored, dismal, dove-colored, dove-gray, drab, drabness,
   drear, drearisome, dreary, dull, dullness, dun, dusty, elderly,
   etiolated, experienced, exsanguinated, exsanguine, exsanguineous,
   faded, faint, fallow, flat, foggy, funebrial, funereal, ghastly,
   glaucescence, glaucescent, glaucous, glaucousness, gloomy, glum,
   grave, gray, gray with age, gray-black, gray-brown, gray-colored,
   gray-drab, gray-green, gray-haired, gray-headed, gray-spotted,
   gray-toned, gray-white, grayed, grayish, grayishness, grayness,
   grim, griseous, grizzle, grizzled, grizzly, grown old, haggard,
   hoar, hoary, hueless, humdrum, hypochromic, iron-gray, lackluster,
   lead-gray, leaden, leadenness, livid, lividity, lividness, lurid,
   lusterless, mat, mature, mealy, misty, monotonous, mouse-colored,
   mouse-gray, mousiness, mousy, muddy, murky, neutral, neutral tint,
   old, old as Methuselah, overcast, paint, painted pony, pale,
   pale as death, pale-faced, pallid, pasty, patriarchal, pearl,
   pearl-gray, pearly, piebald, pinto, repetitive, roan, sad, sallow,
   same, samely, saturnine, senectuous, sickly, silver, silver-gray,
   silvered, silveriness, silvery, skewbald, slate-colored, slatiness,
   slaty, smoke-gray, smokiness, smoky, sober, soberness, solemn,
   somber, somberness, sombrous, sooty, sorrel, steel-gray, steely,
   stone-colored, sunless, tallow-faced, taupe, tedious, toneless,
   triste, uncolored, unrelieved, venerable, wan, washed-out, waxen,
   weak, weariful, wearisome, weary, whey-faced, white,
   white with age, white-bearded, white-crowned, white-haired, wise,
   wrinkled, wrinkly, years old