Nonce means 'for the present time' or 'for a single occasion or purpose', although the word is not often found in general use.
In security engineering, a nonce is a 'number used once'. It is often a random or pseudo-random number issued in an authentication protocol to ensure that old communications cannot be reused in 'repeat attacks'.
In the UK the term nonce is a slang word used to refer to a paedophile.