The Collaborative International Dictionary of English v.0.48:

Epididymis \Ep`i*did"y*mis\, n. [NL., fr. Gr. ?; 'epi` upon + ?
   testicle.] (Anat.)
   An oblong vermiform mass on the dorsal side of the testicle,
   composed of numerous convolutions of the excretory duct of
   that organ. -- Ep`i*did"y*mal, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

epididymis
    n 1: a convoluted tubule in each testis; carries sperm to vas
         deferens