Monotreme

monotreme \ˈmä-nə-ˌtrēm\ noun: any of an order (Monotremata) of egg-laying mammals comprising the platypuses and echidnas

Etymology: New Latin Monotremata, from Greek mon- one, single + trēmat-, trēma hole, opening

The “one hole” or “single opening” referred to by the name monotreme is the cloaca, which handles urination, defecation and reproduction for the critter.