I still use “fortnight” and “fortnightly”, at least partially because so many of the locals don’t seem to know the difference between bi-weekly/-monthly/-ennially and **semi-**weekly/-monthly/-annually…
I’ve heard it in the UK but not in the US in the last few decades…
It originated in the old Li’L Abner comic strip. I doubt that a more specific origin was ever given, but I’m pretty sure that it was derived from “I’d rather,” as you surmised.
Really? How exactly is a single word that just means “two weeks” useful generally (or at least more so than the phrase “two weeks”)? Can you give examples?
Does a word become archaic if it’s being used only currently by a given group? The reason I ask is that “aye” and “aye, aye” are both still in current use within the Navy (and so I hear, the Coast Guard.). I can quite readily accept that it’s not common currency outside those circles, but I’d not consider it archaic, no more than I’d consider “scuttlebutt,” or “head*” to be archaic.
*The bathroom, toilet or WC.
ETA: Leaper, I think you’ll have to admit that talking about speeds in furlongs per fortnight just offers something that you can’t get by talking about feet per two week period.