The Collaborative International Dictionary of English v.0.48:

Diaphanous \Di*aph"a*nous\, a. [Gr. ?, fr. ? to show or shine
   through; dia` through + ? to show, and in the passive, to
   shine: cf. F. diaphane. See Phantom, and cf. Diaphane,
   Diaphanic.]
   Allowing light to pass through, as porcelain; translucent or
   transparent; pellucid; clear.
   [1913 Webster]

         Another cloud in the region of them, light enough to be
         fantastic and diaphanous.                --Landor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

diaphanous
    adj 1: 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]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "diaphanous":
   airy, attenuate, attenuated, boyish, clear, clear as crystal,
   cloudless, crystal, crystal-clear, crystalline, delicate, diaphane,
   diluted, ethereal, filmy, fine, fine-drawn, finespun, flimsy,
   frail, gauzy, girlish, gossamer, gossamery, gracile, insubstantial,
   lacy, light, light-pervious, lightish, lightsome, limpid, lucent,
   lucid, luculent, misty, nonopaque, papery, peekaboo, pellucid,
   rare, rarefied, relucent, revealing, see-through, serene, sheer,
   slender, slenderish, slight, slight-made, slim, slimmish, slinky,
   small, subtle, svelte, sylphlike, tenuous, thin, thin-bodied,
   thin-set, thin-spun, thinnish, threadlike, translucent, translucid,
   transparent, transpicuous, unclouded, unobscured, vague,
   wasp-waisted, watered, watered-down, watery, weak, willowy,
   wiredrawn, wispy