1. either of a pair of glands located on either side of the male urinary bladder that open into the vas deferens and that secrete many components of semen during ejaculation;
WordNet (r) 3.0 (2006):
seminal vesicle
n 1: either of a pair of glands located on either side of the
male urinary bladder that open into the vas deferens and
that secrete many components of semen during ejaculation