Interesting how the word differs from one side of the pond to the other. When I lived in a British colony in Africa in the early 70's I soon discovered "bum" meant "butt" or "ass" to most of the expats from Britain, and those they influenced.

So it was a bit amusing when a talented African singer/songwriter asked me what the meaning was of an American tramping song which had as part of the refrain "... go bum again, go bum again" ! Took me a while to explain about bums and hobos, etc.