Etymology 1

Noun

1. The one or single occasion; the present reason or purpose (now only in for the nonce).

   Unsourced:

   • That will do for the nonce, but we'll need a better answer for the long term.

   1857, Anthony Trollope, Barchester Towers, chapter 6:

   • 'Idiot!' exclaimed the doctor, who for the nonce was not capable of more than such spasmodic attempts at utterance.

2. 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. A sex offender, especially of children; a paedophile.

   That bloke who lives at number 53A is a nonce!

4. A stupid or worthless person.

Noun

1. A datum constructed so as to be unique to a particular message in a stream, in order to prevent replay attacks.

   In this protocol we use the serial number of the message as a nonce.

2. In a security engineering context, a value used only once.
   • 1999, Network Working Group, RFC 2617 -- HTTP Authentication: Basic and Digest Access Authentication, The Internet Society, page 22,

     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.