Definition of "bronco"

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