Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
bush, bush league (adjs., nn.)
Bush in this sense is actually a clipped form of the compound bush league, meaning “second rate,” “cheap,” from its use as a jargon name for the minor leagues in baseball, especially in the first half of the twentieth century. The terms suggest the unpolished manners, the ignorance, and the lack of “class” thought by those who had made it to the major leagues to be characteristic of life in the boondocks. Both terms are slang, having grown beyond the jargon of baseball: The way he behaved to his colleagues was strictly bush [league].
