Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
bum (adj., n., v.)
The noun is an Americanism, meaning “a hobo or vagrant,” and in that use it is Standard. In compounds such as ski bum, meaning “someone who spends all his or her time skiing and hanging around ski lodges,” it is Conversational. As an adjective, it means “incompetent,” as in She’s a bum skater, or “poor quality,” as in We had a bum meal at that place, or “damaged or injured,” as in I’ve got a bum shoulder; all these senses are slang. Among idioms the noun provides to get or give the bum’s rush, meaning “to be thrown out,” or “to throw someone out,” and to be on the bum, meaning “to be wandering, living off the land”; these are slang. The idioms to bum around, meaning “to wander aimlessly,” and to bum out, especially reflexively, as in That really bums me out, meaning “That really irritates me,” are also slang. In British English, the noun bum means “buttocks” (see BUTTOCKS).
