- 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.
- A temporary egg pouch in various fishes and crustaceans.
[Late Latin marsūpium, pouch, from Latin marsīpium, marsuppium, from Greek marsippion, marsuppion, diminutive of marsippos, marsuppos, purse, perhaps of Iranian origin, akin to Avestan marsū-, belly, paunch.]





