#semantle

Okay, so today's answer was: remain

And you might expect it's a weird orphan of sorts.

"Main" as a verb these days is more of a modern back-formation after all. One context is a re-shortening of the compound word "mainline", used in the context of drugs, but then expanded out to any addiction (ie: you might mainline TV all day in the same way that an addict mains heroin all day). The other context that I see main as a verb in is pretty much a game thing - When a game has multiple classes/playstyles/modes/etc., you can *main* a specific one of those - A strong preference over all others, but not necessarily 100% exclusive. "I main Reaper in Overwatch"; "I main Tank for group stuff in MMOs", for example.

So maybe the original use of "main" as an English verb that the re- prefix was applied to was lost to time?

Well, here's the thing. It never existed in the first place.

Main and remain are completely etymologically unrelated.

Even going back to Proto-Indo-European, it appears as though they stem from entirely separate roots.

They're the result of a bit of meaning-divergence and then spelling/pronunciation-convergence

Main, in the English sense is a adjective and noun (with occasional/specific context usage as an adverb, and the later back-formation of the verb) derived from a Germanic (most likely Old Norse) source, related to strength, power, and eventually stemming from those, prominence. It is an old word that existed (in some form) in Old English prior to 900 CE.

There was no verb form to prefix.

Remain, in the English sense, didn't appear until sometime between 1375-1425, and was a verb (and noun, though generally with some modification in English, ie: remains/remainder/remnant) adapted from French. It has Latin roots, which are believed to go further back to Persian, with a Greek intermediary.

It actually came about as a bit of a pronunciation/stress change on the French word remanoir, with the emphasis being moved to the prefix.

Now, the re- prefix means "back", which makes it a little redundant with manoir and the Latin root manere, which also mean "to stay/ to remain" - We do have "stay back" in English, so that's kind of the same idea - The repetition of ideas for emphasis in-context.

But, that meant that manoir as an independent word was easy enough to discard for English.

Except, you might notice a similarity to another English word there. And you'd be right. The noun meaning of manoir, as "a dwelling / a place for remaining/staying" did carry on into English as "manor" and other related words like "mansion" and "manse".

In a weird bit of re-convergence, you could describe a manor house on an estate as the main house, taking the Norse-derived adjective and turning the likewise-Germanically-derived "house" and arriving at a more similar-sounding / meaning as the French-derived manor/mansion by sheer coincidence as the two sources of the "main"/"man-" sound are completely etymologically unrelated.