neurilemma

from WordNet (r) 3.0 (2006)

neurilemma
    n 1: thin membranous sheath around a nerve fiber [syn:
         {neurolemma}, {neurilemma}]

from The Collaborative International Dictionary of English v.0.48

Neurilemma \Neu`ri*lem"ma\, n. [NL., from Gr. ney^ron nerve + ?
   peel, skin.] (Anat.)
   (a) The delicate outer sheath of a nerve fiber; the primitive
       sheath.
   (b) The perineurium.
       [1913 Webster]