A nonce word (from the 16th-century phrase "for the nonce," meaning "for the once") is a lexeme created for temporary use, to solve an immediate problem of communications. Someone attempting to describe the excess water on a road after a storm was heard to call it a "fluddle" -- she meant something bigger than a puddle but smaller than a flood. The newborn lexeme was forgotten (except by a passing linguist) almost as soon as it was spoken. It was obvious from the jocularly apologetic way in which the person spoke that she did not consider "fluddle" to be a "proper" word at all. There was no intention to propose it for inclusion in a dictionary. As far as she was concerned, it was simply that there seemed to be no word in the language for what she wanted to say, so she made one up, for the nonce. In everyday conversation, people create nonce-words like this all the time.
David Crystal, British linguist, _The Cambridge Encyclopedia of the English Language_, 1995