nonce

nonce · noun, adjective¹

1. Middle English · derived fromto þen anes
2. Middle English · inherited fromnonse
3. English todaynonce

Inherited from Middle English nonse, nones, a rebracketing of Middle English to þen anes, for þen anes (to/for the once (i.e., the one occasion or instance)), from the dative singular neuter of þe. The cryptography sense is commonly said to be a contraction of number used once, although this is probably incorrect.

nonce · noun²

1975. Unknown, derived from British criminal slang. Several origins have been proposed; possibly derived from dialectal nonce, nonse (“stupid, worthless individual”) (but this cannot be shown to predate nonce "child-molester" and is likely a toned-down usage of the same insult), or Nance, nance (“effeminate man, homosexual”), from nancy or nancyboy. The rhyme with ponce has also been noted. As prison slang also said to be an acronym for "Not On Normal Communal Exercise" (Stevens 2012), but this is likely a backronym.

First known use, by meaning

• 1975 A sex offender, especially one who is guilty of sexual offences against children.
• 2000 A police informer, one who betrays a criminal enterprise
• 2002 A stupid or worthless person.