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1690s, with -al (1) + Modern Latin marsupialis "having a pouch," coined from Late Latin marsupium "pouch, purse" (Classical Latin marsuppium), from Greek marsipion, diminutive of marsipos "bag, pouch," of foreign, possibly oriental, origin. As a noun from 1805.
Any of various mammals of the order Marsupialia, whose young are very undeveloped when born and continue developing outside their mother's body attached to one of her nipples. Most marsupials have longer hindlegs than forelimbs, and the females usually have pouches in which they carry their young. Kangaroos, opossums, and koalas are marsupials.