marsupium

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

• noun An external pouch or fold on the abdomen of most female marsupials, containing the mammary glands and in which the young continue to develop after leaving the uterus.
• noun A temporary pouch in certain fishes, amphibians, and invertebrates in which eggs are carried until hatched.

from The Century Dictionary.

• noun In Roman antiquity, a purse of the kind usually borne in the hand of Mercury, and indicating his character as god of gain.
• noun In medicine, a sack or bag in which any part of the body is fomented.
• noun In zoology, a purse- or pouch-like receptacle for the eggs or young, more external than any of the proper organs of gestation; a brood-pouch of any kind.
• noun In anatomy, the alar ligaments (which see, under alar).

from the GNU version of the Collaborative International Dictionary of English.

• noun The pouch, formed by a fold of the skin of the abdomen, in which marsupials carry their young; also, a pouch for similar use in other animals, as certain Crustacea.
• noun The pecten in the eye of birds and reptiles. See pecten.

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

• noun The external pouch in which female marsupials rear and feed the young
• noun A brood pouch in some fishes, crustaceans and insects in the family Monophlebidae

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

• noun an external abdominal pouch in most marsupials where newborn offspring are suckled