The Collaborative International Dictionary of English v.0.48:

Fibrous \Fi"brous\ (f[imac]"br[u^]s), a. [Cf. F. fibreux.]
   Containing, or consisting of, fibers; as, the fibrous coat of
   the cocoanut; the fibrous roots of grasses. --
   Fi"brous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fibrous
    adj 1: having or resembling fibers especially fibers used in
           making cordage such as those of jute [syn: hempen,
           fibrous]
    2: (of meat) full of sinews; especially impossible to chew [syn:
       fibrous, sinewy, stringy, unchewable]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "fibrous":
   capillary, cartilaginous, chewy, cirrose, cirrous, cohesive,
   coriaceous, durable, fibered, fibroid, flagelliform, flossy,
   funicular, gossamery, gristly, hairlike, hairy, hard, hardy,
   lasting, leatherlike, leathery, ligamental, resistant, ropy, silky,
   sinewy, stiff, stringy, strong, stubborn, taeniate, taeniform,
   tenacious, threadlike, thready, tough, tough as leather, untiring,
   vigorous, viscid, wiry