Several months ago, I did words that ended in -ress. Two I skipped were mattress and buttress, as they weren’t related to the others. So let’s look at them now! Because I have no other ideas.
Mattress is surprisingly old, having shown up in the late thirteenth century. It comes from the Old French materas, which comes from the Italian word materasso, just mattress. That’s the word that comes from Latin, in this case the Medieval Latin matracium, which in turn was taken from Arabic, where it was al-matrah, cushion. This is especially unusual because Latin prefers stealing its words from Greek.
Buttress first showed up in the early fourteenth century as a noun and the late fourteenth century as a verb. It comes from the Old French arc botrez, flying buttress. Not sure why it had to be flying, but there you go. It’s supposed to be from bouter, to thrust against, a Frankish word from the Proto Germanic butan, which in turn comes from the Proto Indo European bhau-, to strike. Which is the origin word for butt! But not the one that means your rear end. The one that’s part of head butt. Kind of disappointing, really.