The Collaborative International Dictionary of English v.0.48:

Vas \Vas\, n.; pl. Vasa. [L., a vessel. See Vase.] (Anat.)
   A vessel; a duct.
   [1913 Webster]

   Vas deferens; pl. Vasa deferentia. [L. vas vessel +
      deferens carrying down.] (Anat.) The excretory duct of a
      testicle; a spermatic duct.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vas deferens
    n 1: a duct that carries spermatozoa from the epididymis to the
         ejaculatory duct [syn: vas deferens, ductus deferens]