The word usher was borrowed into the English language in 1386, when it was spelled ussher. Through Anglo-Norman, it traces to the Old French noun ussier, which had definitions of "porter" or "doorman" - still pretty similar to today. That's from Vulgar Latin ustiarius and Latin ostiarus, which both also meant "doorman". The root of ostiarus is ostium, or "door", and it all eventually derives from the Proto-Indo-European reconstruction os, meaning "mouth" (the idea was that both are entrances or openings of a sort). Os also gave us the words oral, Oslo ("river mouth" in Old Norse), oscitant, orifice, orator, and many other terms that have to do with gaps and mouths in general. According to Google NGrams, literary usage of the word usher was highest in the 1500s and has been trending downwards since.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.