WordNet (r) 3.0 (2006):

threadlike
    adj 1: thin in diameter; resembling a thread [syn:
           filamentous, filiform, filamentlike, threadlike,
           thready]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "threadlike":
   airy, attenuate, attenuated, boyish, capillary, cirrose, cirrous,
   delicate, diaphanous, diluted, ethereal, fibered, fibroid, fibrous,
   fine, fine-drawn, finespun, flagelliform, flimsy, flossy, frail,
   funicular, gauzy, girlish, gossamer, gossamery, gracile, hairlike,
   hairy, insubstantial, lacy, ligamental, light, misty, papery, rare,
   rarefied, ropy, silky, slender, slenderish, slight, slight-made,
   slim, slimmish, slinky, small, stringy, subtle, svelte, sylphlike,
   taeniate, taeniform, tenuous, thin, thin-bodied, thin-set,
   thin-spun, thinnish, thready, vague, wasp-waisted, watered,
   watered-down, watery, weak, willowy, wiredrawn, wiry, wispy