nonce

Etymology 1

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.

noun

1. The one or single occasion; the present reason or purpose (now only in for the nonce).
   That will do for the nonce, but we'll need a better answer for the long term.
   … Dunce, / Dotard, a-dozing at the very nonce, / After a life spent training for the sight! 1855, Robert Browning, Childe Roland to the Dark Tower Came, section XXX
   'Idiot!' exclaimed the doctor, who for the nonce was not capable of more than such spasmodic attempts at utterance. 1857, Anthony Trollope, chapter 6, in Barchester Towers
2. (lexicography) A nonce word.
   I had thought that the term was a nonce, but it seems as if it's been picked up by other authors.
3. (cryptography) A value constructed so as to be unique to a particular message in a stream, in order to prevent replay attacks.
   The protocol opens with A communicating in clear to AS his own claimed identity and the identity of the desired correspondent, B, together with A's nonce identifier for this transaction, I_(A1). ("Nonce" means "used only once.") December 1978, Roger M. Needham, “Using Encryption for Authentication in Large Networks of Computers”, in Communications of the ACM, volume 21, number 12
   The information gained by the eavesdropper would permit a replay attack, but only with a request for the same document, and even that may be limited by the server's choice of nonce. 1999, Network Working Group, RFC 2617 – HTTP Authentication: Basic and Digest Access Authentication, The Internet Society, page 22
   Both CCM and GCM require a unique nonce (N used once) value to maintain their privacy and authenticity goals. 2006, Tom St Denis, Cryptography for Developers, page 340
   The main idea with the challenge-response type of authentication protocol is that the challenge sent by the server is used only once (referred to as a cryptographic nonce, which means “number used once”). 2012, Steven Anson, Mastering Windows Network Forensics and Investigation

adj

1. One-off; produced or created for a single occasion or use. Denoting something occurring once.
   But particular men are not stereotyped for jobs nor particular desks (as against others) to sit at - the standard here is nonce. 1977, Robert Anderson Hall, David Morris Feldman, Homenaje a Robert A. Hall, Jr, page 75
   Dickinson's association of heliotrope with Mary Bowles was nonce and fleeting, but the subject of gardens was always a safe one on which to address her: “How is your garden – Mary? Are the Pinks true –?” 2009, Judith FARR, Louise Carter, The Gardens of Emily Dickinson, page 55
   Poplack et al. (1988, 57) found that 65% of their types were nonce and only 7% of the types were considered widespread. 2010, Susana Rivera-Mills, Juan Antonio Trujillo -, Building Communities and Making Connections, page 191
   Some of the single-citation terms appeared to be nonce formations, that is, created for the occasion. 2018, James Lambert, “A multitude of ‘lishes’: The nomenclature of hybridity”, in English World-Wide, page 16

Etymology 2

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.

noun

1. (Britain, derogatory) A sex offender, especially one who is guilty of sexual offences against children.
   1989 "assorted nonces, ponces and murderers, 'the worst men in the world' … on the nonce wing, where the child-killers, molesters and various perverts have to be protected from the other prisoners." (New Statesman, New Society, Volume 2, Statesman & Nation Publishing Company Limited)
2. (by extension) A pedophile.
   ‘He's a nonce[. A] nonsense merchant, a paedophile[,’ Terry explained.] 2004, Jeffery Archer, A Prison Diary, St. Martin's Publishing Group, page 72
3. (Britain, prison slang, derogatory) A police informer, one who betrays a criminal enterprise
4. (Britain, slang, derogatory) A stupid or worthless person.
   Shut it, ya nonce!