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]