c.1300, from Latin rhinoceros, from Greek rhinokeros, from rhinos "nose" (a word of unknown origin) + keras "horn" (see kerato-). Shortened form rhino is first attested 1884.
What is the plural of rhinoceros? ... Well, Liddell and Scott seem to authorize 'rhinocerotes,' which is pedantic, but 'rhinoceroses' is not euphonious. [Sir Charles Eliot, "The East Africa Protectorate," 1905]