The Collaborative International Dictionary of English v.0.48:
Filamentous \Fil`a*men"tous\, a. [Cf. F. filamenteux.] Like a thread; consisting of threads or filaments. --Gray. [1913 Webster]WordNet (r) 3.0 (2006):
filamentous adj 1: thin in diameter; resembling a thread [syn: filamentous, filiform, filamentlike, threadlike, thready]