In linguistics, a fake word invented to fill a specific, immediate language need. One envisions a child making up a word to refer to something her or she doesn’t know the actual name of.
“for the none” is Middle English for “for this one time.”
The term is also used in programming to refer to a temporary, relatively unique value that would be hard to guess and signifies something.
In very general terms, “nonce” means something random and intentionally temporary.