The Collaborative International Dictionary of English v.0.48:

Micropyle \Mi"cro*pyle\, n. [Micro- + Gr. ? gate, orifice: cf.
   F. micropyle.] (Biol.)
   (a) An opening in the membranes surrounding the ovum, by
       which nutrition is assisted and the entrance of the
       spermatozoa permitted.
   (b) An opening in the outer coat of a seed, through which the
       fecundating pollen enters the ovule. -- Mi*crop"y*lar,
       a.
       [1913 Webster]

WordNet (r) 3.0 (2006):

micropyle
    n 1: minute opening in the wall of an ovule through which the
         pollen tube enters