No, sackbut isn't a Shakespearean insult for a steatopygous individual; it's the precursor to the modern trombone used during the medieval and Renaissance eras.
Image via WikipediaThe word comes from the Middle French saqueboute, which itself comes from Old French saquier, "to pull," and bouter, "to push." After all, that's how you play it — by pushing and pulling.
The etymology of the "pull-push" bears a resemblance to that of the "soft-loud" — the piano, which is more accurately called the pianoforte, derived from the Italian words for "soft" and "loud": piano and forte, respectively. The immediate precursor to the pianoforte was, strangely enough, the fortepiano, the instrument that Haydn and Mozart wrote for. Earlier keyboard instruments, like the harpsichord, were plucked, and so did not have a wide range of dynamics. The fortepiano introduced mechanisms that, for the first time, allowed keyboardists to control the volume of the notes by how hard they pressed the keys. So the fact that the instrument could play loudly and softly, forte e piano, was the selling point.
And the rest is music history.
But back to the sackbut. As horrible as sackbut might sound, if those musicians of old had decided to put the "push" before the "pull," it might have been called the even worse-sounding butsack.
I almost wish they had.