I’m voting for thrice. After all, we kept once and twice, so why not bring back thrice?
I also think hence, thence, and whence should be candidates for revival. I’m all for simple, one syllable words making a come back.
Also, given the state of the world these days, I think I’m going to try to drop blackguard, rapscallion and knave in a few conversations.
I use thrice and hence, so I’m either way older than I feel, or way out of touch. Sometimes I’ll use thence or whence, but only because I’m lazy and I forget that other people won’t understand me. Of course using them in literary fashion is par for the course.
Now if we’re speaking “American,” I’d strongly favor re-introducing “fortnight.” Thanks to my interest in old literature I’ve always understood the meaning, but working with Aussies and Brits the last several years really made me understand the practicalness of actually using it. Fuck “stone,” though, I mean, really, the metric UK still uses stone???
I’d like to attack collective nouns, too. I hate to admit it, but I’ve become really fond of “product development are” and “such and such team are”; it’s subtle, but gives a real sense of plurality and collectiveness in the actions that are being performed.
And I hate “you guys” (Michigan), “y’all,” etc. Maybe it’s time to reintroduce the distinction between “you” and “thou.”
I definitely use “hence”, and use “whence” too, but more for a slightly amusing effect. So we might as well bring back “thence” just to have the set of three.
Yes to bringing back “thrice”. However, it might be necessary to offer a prize for someone using it in a cheerful way, as it is so much associated with “woe, woe, and thrice woe!”.
How about bringing back “sennight”? 
Thrice married is a common way to refer to someone who has married 3 times. Similarly, thrice divorced.
Hence and whence are not uncommon. Thence, I’l grant.
None of those is out of use.
If we’re talking archaic, we should reach back to “wherefore” or something like that.
Lustrum.
And blushet.
'Tis, 'twas and 'twere.
How about “forsooth”? I like that one. 'Tis a word that doth please me greatly.
I like smite.
I have two: dear, meaning expensive; and strumpet, an old word for prostitute.
Dear is obsolete or archaic? It’s in common currency in my variant of English (which is Hiberno-English) and it’s also common in BrE and its variants and dialects. I had no idea it was considered archaic or obsolete in AmE.
Nextly.
As in:
Firstly: blah
Nextly: blah blah blah.
Furthemore: blah blah.
Lastly: blah.
It’s a real word, and it exists in the more complete editions of the OED. I have been using it for years, and as a result, my kids do too - my daughter got marked down by her English teacher for using it - I did the full Helicopter Parent on that one.
Venison’s dear, isn’t it?
(Credit: Jimmy Carr)
I’ve been using “blackguard” for years now.
I’d be happy if we could bring back “ne’er-do-well” and “no-good-nik” while we’re at it.
I rather like verily; hither and thither; whence and whither; and forthwith.
How much more satisfying it would be to shout out “Bring that report hither, forthwith,” than to say “Bring that report over here, now”.
It would be even more satisfying if I could toss in a “varlet” at the end of the command.
I’d like to bring back the original definition of “nice” (meaning “foolish, stupid, senseless”) so I could say things like, “Look at those nice parents who refuse to vaccinate their kids!”
Forwaked: to be roused from sleep before time. From the Wakefield Mystery Play, when the shepherds are grousing to each other about their wives, kids and jobs:
We found it particularly useful as new parents; people whose neighbours enjoy early morning Harley rides or those on shift work whose family call during the day may also find occasion to use it.
yclept
as in
The Master, yclept Cecil Adams, wrote …
In this age of texting and other electronic communication, it would be nice to see the return of signatures like “Your obedient and humble servant” (not so much an archaic word as an archaic phrase)