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]