also broncho, 1850, American English, "untamed or half-tamed horse," from noun use of Spanish bronco (adj.) "rough, rude," originally a noun meaning "a knot in wood," perhaps from Vulgar Latin *bruncus "a knot, projection," apparently from a cross of Latin broccus "projecting" (see broach (n.)) + truncus "trunk of a tree" (see trunk (n.)). Bronco-buster is attested from 1886.
A young male not accustomed to nor complaisant in homosexual relations (1970s+ Homosexuals)
[fr Spanish bronco, ''coarse, rough'']
North American wild or Indian-tamed horse, descended from horses taken to the New World by the Spanish in the 16th century. The name comes from that of an Indian tribe of eastern Washington and Oregon that was known for the small horses it bred.