It’s also UK slang for peadophile, so be careful that everyone understands you are talking about cryptography not sex offenders if you use the word in public as there could be a nasty misunderstanding!

There's a lot of vocabulary like that. I've had conversations about ensuring a daemon reaped zombie children in public before we realized what it sounded like.

Then there's a lot of master/slave terminology.

Is the term that old? I was told it literally meant N(umber)once.

Yes, the construction "for the nonce" goes back to the Middle Ages. The concept of a "nonce word" goes back to 1884, according to this article.

https://www.dailywritingtips.com/nonce-words-for-the-nonce-a...

I'm not necessarily arguing there's shared etymology, but consider 'for the nonce' - it's not merely a made up word used exclusively in cryptography.