Fibril

from WordNet (r) 3.0 (2006)

fibril
    n 1: a very slender natural or synthetic fiber [syn: {fibril},
         {filament}, {strand}]

from The Collaborative International Dictionary of English v.0.48

Fibril \Fi"bril\, n. [F. fibrille, dim. of fibre, L. fibra.]
   A small fiber; the branch of a fiber; a very slender thread;
   a fibrilla. --Cheyne.
   [1913 Webster]