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):

fibrousness
    n 1: the quality of being fibrous [syn: fibrosity,
         fibrousness]