seminal vesicle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Either of a pair of pouchlike glands situated on each side of the male urinary bladder that secrete seminal fluid and nourish and promote the movement of spermatozoa through the urethra.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy One of two simple tubular glands located behind the male urinary bladder, responsible for the production of about sixty percent of the fluid that ultimately becomes semen.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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