c. 1300, from Latin rhinoceros, from Greek rhinokeros, literally "nose-horned," from rhinos "nose" (a word of unknown origin) + keras (genitive keratos) "horn of an animal," from PIE root *ker- (1) "horn; head." Related: Rhinocerotic.
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]