The Collaborative International Dictionary of English v.0.48:

Gossamer \Gos"sa*mer\, n. [OE. gossomer, gossummer, gosesomer,
   perh. for goose summer, from its downy appearance, or perh.
   for God's summer, cf. G. mariengarr gossamer, properly Mary's
   yarn, in allusion to the Virgin Mary. Perhaps the E. word
   alluded to a legend that the gossamer was the remnant of the
   Virgin Mary's winding sheet, which dropped from her when she
   was taken up to heaven. For the use of summer in the sense of
   film or threads, cf. G. M[aum]dchensommer, Altweibersommer,
   fliegender Sommer, all meaning, gossamer.]
   [1913 Webster]
   1. A fine, filmy substance, like cobwebs, floating in the
      air, in calm, clear weather, especially in autumn. It is
      seen in stubble fields and on furze or low bushes, and is
      formed by small spiders.
      [1913 Webster]

   2. Any very thin gauzelike fabric; also, a thin waterproof
      stuff.
      [1913 Webster]

   3. An outer garment, made of waterproof gossamer.
      [1913 Webster]

   Gossamer spider (Zool.), any small or young spider which
      spins webs by which to sail in the air. See Ballooning
      spider.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gossamer
    adj 1: characterized by unusual lightness and delicacy; "this
           smallest and most ethereal of birds"; "gossamer shading
           through his playing" [syn: ethereal, gossamer]
    2: so thin as to transmit light; "a hat with a diaphanous veil";
       "filmy wings of a moth"; "gauzy clouds of dandelion down";
       "gossamer cobwebs"; "sheer silk stockings"; "transparent
       chiffon"; "vaporous silks" [syn: diaphanous, filmy,
       gauzy, gauze-like, gossamer, see-through, sheer,
       transparent, vaporous, vapourous, cobwebby]
    n 1: a gauze fabric with an extremely fine texture
    2: filaments from a web that was spun by a spider [syn:
       cobweb, gossamer]

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "gossamer":
   air, airy, animal fiber, artificial fiber, attenuate, attenuated,
   boyish, bubble, cambric tea, capillament, chaff, chip, cilium,
   cirrus, clear, clear as crystal, cobweb, cork, crystal,
   crystal-clear, crystalline, dainty, delicate, denier, diaphane,
   diaphanous, diluted, dishwater, down, downy, dust, ether, ethereal,
   fairy, feather, fiber, fibrilla, filament, filamentule, filmy,
   fine, fine-drawn, fine-grained, finespun, flagellum, flimsy, flue,
   fluff, fluffy, foam, frail, froth, fuzz, fuzzy, gauzy, girlish,
   gossamery, gracile, gruel, hair, hank, house of cards,
   insubstantial, lacy, light, light-pervious, limpid, lucid,
   matchwood, milk and water, misty, mote, nonopaque, papery,
   peekaboo, pellucid, pubescent, rare, rarefied, reed, refined,
   revealing, rope of sand, sand castle, satin, satiny, see-through,
   sheer, silky, skein, slender, slenderish, slight, slight-made,
   slim, slimmish, slinky, small, smooth, sponge, spume, strand,
   straw, subtle, suture, svelte, sylphlike, tendril, tenuous, thin,
   thin-bodied, thin-set, thin-spun, thinnish, thistledown, thread,
   threadlet, threadlike, transparent, transpicuous, unclouded, vague,
   velutinous, velvety, wasp-waisted, water, watered, watered-down,
   watery, weak, web, willowy, wiredrawn, wispy