THE OED appropriates Samuel Johnson’s definition (“The buttocks, the part on which we sit”), notes that it is “Not in polite use,” and offers a first citation from 1387.
The Google Ngram below shows the relative use of his bum (blue), her bum (red) and my bum (green) in American English books published from 1800-2008.
The chart is interesting to me for two reasons. First, it shows a fairly common pattern of frequent use of a British expression (or spelling) around 1800, declining for a hundred years (give or take), then increasing, slowly at first, then more rapidly in the last twenty or thirty years, the age of NOOBs. More subtle and surprising, to me, is the relative frequency of the three expressions. At first her is the most common by far and my is barely (no pun intended) used. But now the three forms are all about equal. Surely someone can make of this a monograph on sexuality and identity!
Runway falls don’t get any more straightforward than this: blame the shoes — again. The beauty of this clip, however, is the drunken-looking wobbly-ness of her recovery. The model in question falls on her bum, but looks like she might have bumped her head and seen some little birdies. (Time.com, February 13, 2009)/Up first was Rob Kardashian with a jazz-influenced cha-cha to “Walk Like A Man” from “Jersey Boys.” In practice, he asks partner Cheryl Burke to teach him to shake his bum like pro Maksim Chmerkovskiy. (Baltimore Sun, “Dancing with the Stars” blog, October 24, 2011)
Bum is definitely a Britishism, but is bottom (a word with which, surprisingly, it has nothing in common etymologically)? The OED dates it to about 1800 and cites all British sources, including this from Carlyle’s 1837 The French Revolution: “Patriot women take their hazel wands, and fustigate … broad bottoms of priests.”
Bottom is certainly commonly used in the U.S. now, often (oddly) either fully or semi-lasciviously or in addressing children, but also more straightforwardly, as in this 2003 New Yorker review of a Martha Graham dance performance: “I saw that Gary Galbraith, when he played the Minotaur, was provided with a pair of shorts that covered his bottom.“
I would appreciate your thoughts on whether bottom is a Britishism, as well as a vote in the poll below.
notoneoffbritishisms.com 
I am british, so I won’t vote.
`Bottom’ is certinly British, but it never occurred to me that it might be a Britishism. What word do Americans use when talking to their children?
To Rchrd West: my choice in talking to children(usually my own), is “butt,” as in “Get off your butt and do something!” While I think that “bum” is perfectly OK and certainly understandable in American vernacular, it remains no more than a third or fourth tier synonym, behind “ass,” “butt,” and “backside,” It’s also a contextual, educational, socio-economic and age-driven choice. I hope I haven’t given a bum opinion; it’s probably time for me to butt out before I make an ass of myself.
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Behind is often used in the UK;
Yes, I remember ‘behind’ was almost always used in the UK back in the 1960s and 70s. ‘Bum’ came a close second, often between people who are better acquainted with each other.
As swearing has become more acceptable “arse” has become fairly common, albeit sometimes changed to “behind” at the last minute.
I don’t know is anyone else is the same, but I find “my bum” more difficult to say than “her bum”; it feels very stilted and awkward for some reason (should see a doctor, boom boom) so maybe that’s one reason for the discrepancy there? Even “my butt” is easier. Perhaps it’s just me… That’s assuming people would tend to write down just what they say of course.
No not difficult. We were referring to it as behind never arse still won’t, recently started saying bum and prefer it, (from our American and friends.) Try to use it more when you are around close friends. When you use it more but you need to use it more to get passed that point and tell yourself it refer to your bum, you won’t find it awkward or hard. and you will start to prefer it, just give it time I hope this helps you.
“behind” is a polite term, “bum” not so much. Hence the preference for “behind” in schools, etc.
In the US, “bum” is acceptable but slightly cute, possibly because it is a conscious Britishism. “Butt” strikes me as a shade cruder.
Extremely late, I know, but when I was a child (1940s/50s) and even the mildest “rude words” were off limits, the usual words were bottom and backside, but my grandmothers eschewed even those mild words in favour of B T M – pronounced bee tee em (Dylan Thomas uses this in one of the children’s songs in Under Milk Wood: “Hit him with a slipper on his B T M”.) They also referred to women’s underwear as “unmentionables”.
I agree with Keith. When I was growing up in England in the 60s, bottom was the most acceptable polite term term in general conversation. I love the line in ‘A Fish Called Wanda’ where John Cleese’s wife severs her relationship with him by saying, ‘You can stick this marriage up your bottom!’ No one would ever say that in real life. It’s just a joke about bum euphemisms.
In England the article you describe as a Fanny Pack is a Bum Bag; even in polite society. However in England the word ‘fanny’ is a descriptive for a lady’s ‘front bottom’ (female pudenda / labia and vagina combo) and definitely not used in polite society. You can also imagine the outrage and/or confusion when in US TV shows and films a male character is said to have fallen on his fanny! Two nations divided by a common language indeed. Have you covered ‘knocked up’ (in UK woken up early by arrangement, in US made pregnabt) by the way?
Have to add the Shakespearean use of the word here: Puck in A Midsummer Night’s Dream:
“Sometime for three-foot stool mistaketh me;
“Then slip I from her bum, down topples she”
Also the phrase ‘bums on seats’ is in common use in arts and event management parlance – “we need to get bums on seats if we’re going make this show pay”, etc. Quite recently this would have seemed rather coarse, but its edge has been blunted by time. I’ve heard Americans in the UK use this phrase, but having never been to the US, cannot tell whether it’s in use there.
But(t) do not confuse ‘bum’ with ‘to bum’. The preceding ‘to’ makes quite a big difference 🙂
Sometimes used as an expletive as in “Bum!” or “Oh bum!”, similarly you might say “arse!” (less rude than saying “F**k!”
We live in New York and prefer bum bottom is ok but it can mean alot of things. So we changed. We have noticed that more and more people here in New York are using bum as their preferred word which is good to see
I meant to add as well that people now can see it as a perfectly good word to use
When I had a child in 2009, I started hearing other American parents, whom I knew had no direct UK influence (they hadn’t lived there or grown up with a British parent) use “bum” with their babies/toddlers. At that time I had never heard an American use “bum” to mean “buttocks.” I would still reckon that American adults are much more likely to say “my butt” for their posterior than anything else, but some do say “your bum” to their kids (others use tushie, bottom, hiney, other long-standing cutesy words).
Perfectly fine to refer to it as bum. We have noticed alot of our American friends using it now. My 3 year old came home one day and refer to it as his bum, so that is what we all refer to it now. It sounds really cute
Bum came into use in the US after Mike Myers used it heavily on Saturday Night Live with his Stuart character.
I have started to hear and now prefer it, I agree with some of the other comments. To me bum sounds a much nicer word than butt now. I hope in America we start to hear the word butt less and start to use and hear bum more.