This is a word that can really throw you.
I don’t just mean its object, that butch tree, that brute tech, that better-than-catapult that can hurl large stones, small cars, and any old piano or organ through the countryside:
That machine certainly illustrates the value of a good pitcher’s arm, in a warped way. (I may mean warp in the old sense of ‘throw’ – that’s what the Old English word weorpan meant, a sense preserved in weaving; it gained our current sense apparently thought reference to the twisting one may do when throwing, as a pitcher does, not that they had baseball back then. On the other hand, speaking of pitchers and pots, throw – in its Old English version, þrāwan – originally meant ‘twist’ or ‘turn’, a sense preserved in pottery; its sense went deasil where warp went widdershins.) But there is a thing about letting trebuchet loose from your tongue that may throw you off.
Let us trace its trajectory to its current landing. English has had the word since the 1200s; we got it from Old French, which spelled it the same as we do. Old French put it together from two parts: the tre is from Latin trans, while the buchet is a derived from Old French buc meaning the trunk of the body; that word in turn came from an old Germanic root that has come down to modern German Bauch ‘belly’. Put the loose Latin with the hard German and you get something meaning ‘topple’.
And since we got it from French, we say it like French, right? Not so fast. We got it from Old French, in which trebuchet was said with the last syllable identical to how we say Chet as in Chet Baker. And since that works equally well in English, that’s how it got enshrined in our language.
But we went a long time without using these things in war, having discovered other less amusing but more destructive machines (with better range, too). So in modern times, when we encounter one (typically built for amusement), and encounter its name, we see a French word – it really does look French, doesn’t it? – and say it like a French word. Specifically, like an English-accented rendition of trébuchet, which is the modern French descendent of trebuchet, meaning the same thing and said as you would expect.
Now, there are various –et words we got from French that we might think we should say to rhyme with “bay” but actually rhyme with “bet”: Moët, for instance (as in the champagne), which is an old French name that has always had the t pronounced in French; or claret, which was taken long ago from French clairet but is thoroughly anglicized in form, sense, and sound. Trebuchet may seem more like the latter but is actually more like the former (fitting, since a Moët can throw a cork a long distance, whereas a claret cannot). But there is a difference: Moët is still said with the t in French. We have, in general, decided to keep up with modern times, pull trebuchet out of the garage and pay homage to the modern Gauls, and say it to rhyme with “bay.”
“We” does not quite include some dictionaries, though. Which is why, as this little detail has been discovered, a movement is afoot to get Merriam-Webster to add the most popular current pronunciation to its entry.
And where do I stand on this?
I think that I shall never say
A word more swash than trebuchet
(Unless I say it “trebuchet”
[Please be aware I haven’t yet])