Likely the same "butt" as in "buttload", either from Anglo-Norman or from Proto-West Germanic but in any case ultimately from Ancient Greek bouttis via Latin buttis. The names of the ball sports bocce and boccia are from the same source, as are so many languages' words for barrel, cask, bucket, head, and/or pumpkin that I'm not going to bother listing them all, just know that the list includes languages like Ubykh, Armenian, Georgian, Turkish, Kyrgyz, Kazakh, Udmurt, Mongolian, Arabic, Maltese, Irish, unsurprisingly Greek, and seemingly every extant Romance, Germanic, and Slavic language, and quite a few other languages with a lot of loanwords from the aforementioned.

Most relevantly for me is that I had Stewart Clark's "Broken English" books as a kid, which included assorted Bushisms (real or spurious), machine-translated Chinese restaurant menus, and various other "Epic Fails™" with the English language of that ilk. It being a book written for Norwegian audiences, a lot of its pages were dedicated more specifically to collecting anecdotes of Scandinavians using a first-language false friend when speaking English to humorous effect. And so…

[Unreconstructed Pre-Greek substrate] → Ancient Greek bouttis ("cask, barrel") → Latin buttis → Vulgar Latin *buttia → Proto-West Germanic *buttjā → Middle Low German butte → Old Norse bytta ("pail, bucket") → Danish bøtte → Norwegian bøtte

…This is the nearly 3,500 year long Rube Goldberg machine that led to the following probably spurious anecdote of the "Norwegian is bad at English, please laugh because you are Norwegian and good at English" genre of joke, which I personally first encountered in one of Stewart Clark's "Broken English" books:

A Frenchman and a Norwegian are fishing together. The Frenchman catches a huge fish and excitedly asks, "Where shall I put it?"

The Norwegian replies, "Just put it in the butt."

[the two are immediately killed by a rain of drums and cymbals]

You should watch SPARKLE ON RAVEN: The Life of DrillGirl; it is a very good show. {Cēterum|Furthermore} {cēnseō|I think} {iūs auctōris|copyright} {esse dēlendum|must be destroyed}.