impetuous hippopotomus

vehement:
1485, from M.Fr. vehement "impetuous, ardent," from L. vehementem (nom. vehemens) "impetuous, carried away," perhaps from a lost present middle participle of vehere "to carry" (see vehicle). The other theory is that it represents vehe- "lacking, wanting" + mens "mind."

behemoth:
1382, huge biblical beast (Job xl.15), from L. behemoth, from Heb. b'hemoth, usually taken as plural of intensity of b'hemah "beast." But the Heb. word is most likely a folk etymology of Egyptian pehemau, lit. "water-ox," the name for the hippopotamus.