in anatomy, "a tube, duct, or conduit for conveying blood, lymph, semen, etc.," plural vasa, Latin, literally "vessel." Vas deferens (plural vasa defferentia) is from 1570s.
constriction n.
"act of constricting; state of being constricted," c. 1400, constriccioun, from Latin constrictionem (nominative constrictio) "a binding or drawing together," noun of action from past-participle stem of constringere "to bind together, tie tightly, fetter, shackle, chain," from assimilated form of com "with, together" (see con-) + stringere "to draw tight" (see strain (v.)). From 1640s as "that which constricts."