The Collaborative International Dictionary of English v.0.48:

Filar \Fi"lar\, a. [L. filum a thread.]
   Of or pertaining to a thread or line; characterized by
   threads stretched across the field of view; as, a filar
   microscope; a filar micrometer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

filar
    adj 1: related to or having filaments (especially across a field
           of view as in the eyepiece of a telescope); "a filar
           eyepiece"