bronco

Etymology

Borrowed from Spanish bronco (“rough”), 19th c. which in Mexican usage also describes a horse that has not been broken and is still wild.

noun

1. A horse of western North America that is wild or not fully broken.
   Swollen with greatness, slightly afraid lest the noble blood of Nottingham change its mind and leave him at any street corner, Babbitt paraded with Sir Gerald Doak to the movie palace and in silent bliss sat beside him, trying not to be too enthusiastic, lest the knight despise his adoration of six-shooters and broncos. 1922, Sinclair Lewis, “19”, in Babbitt