ep·i·did·y·mis 
(
ĕp
′ĭ-d
ĭd
ə-m
ĭs)
n. pl. ep·i·did·y·mi·des (-m
ĭ-d
ēz
′)
A long, narrow, convoluted tube, part of the spermatic duct system, that lies on the posterior aspect of each testicle, connecting it to the vas deferens.
[Greek epididumis : epi-, epi- + didumoi, twins, testicles, pl. of didumos, double; see dwo- in the Appendix of Indo-European roots.]
ep′i·didy·mal adj.