Such a useful word, bum. In Britain it's a slightly rude word for buttocks - but then referring to the buttocks will always be slightly rude (or slightly embarrassing, anyway) so it gets a lot of use.
There are quite a few bum words that have appeared over the centuries. A bum-roll is a long cushion that was tied round the waist and held out the skirts of a Tudor lady. (Tudor ladies had farthingales, too, but you couldn't wear a farthingale if you were riding a horse. Indeed, sitting down at all was almost impossible).
A bumbailiff is an old slang word for a debt-collector; and bumfluff is a young man's first wispy attempt at a beard.
The American bum, meaning an idler or hobo (what in England we would call a tramp), isn't used in Britain, but we've borrowed one associated meaning: bad musicians here, as in America, play bum notes.
There's one bum word which isn't connected to either of these kinds of bum: a bumboat is a small craft used for ferrying things from a ship to shore.
Word To Use Today: bum. Bum meaning buttocks has been around since the 14th century, though no one knows where it came from before that. Bum meaning homeless person is from the German word bummeln, to loaf. And bum as in bumboat is from the Dutch boomschip, a canoe, from bom, tree.
A bumbailiff is someone who follows you very closely indeed.