Source : Webster's Revised Unabridged Dictionary (1913)

Endoneurium \En`do*neu"ri*um\, n. [NL., fr. Gr. 'e`ndon within +
   ? a sinew, nerve.] (Anat.)
   The delicate bands of connective tissue among nerve fibers.

Source : WordNet®

endoneurium
     n : delicate connective tissue around individual nerve fibers in
         nerve