Source : Webster's Revised Unabridged Dictionary (1913)

Brontotherium \Bron`to*the"ri*um\, n. [NL., fr. Gr. ? thunder +
   ? beast.] (Paleon.)
   A genus of large extinct mammals from the miocene strata of
   western North America. They were allied to the rhinoceros,
   but the skull bears a pair of powerful horn cores in front of
   the orbits, and the fore feet were four-toed. See
   Illustration in Appendix.