The Collaborative International Dictionary of English v.0.48:

Awn \Awn\ ([add]n), n. [OE. awn, agune, from Icel. ["o]gn, pl.
   agnir; akin to Sw. agn, Dan. avne, Goth. ahana, OHG. agana,
   G. agen, ahne, chaff, Gr. 'a`chnh, AS. egla; prob. from same
   root as E. acute. See 3d Ear. [root]1.] (Bot.)
   The bristle or beard of barley, oats, grasses, etc., or any
   similar bristlelike appendage; arista. --Gray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

awn
    n 1: slender bristlelike appendage found on the bracts of
         grasses