plural noun Am·mo·noi·dea \ˌaməˈnȯidēə\

Definition of Ammonoidea

  1. :  an order of extinct chiefly Mesozoic Tetrabranchia comprising cephalopods having an external chambered shell that is either straight or variously curved or coiled — see 1ammonite


\¦amə¦nȯidēən\ adjective or noun

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Origin and Etymology of ammonoidea

New Latin, irregular from Ammonites + -oidea

First Known Use: 1884

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a rounded knoll or a ridge of ice

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