Nonce
Nonce is a new word that one makes up on the spot and uses it once. This new word is not expected to be used again. However, if people start using the new word, then it may become a neologism (roughly synonym with coinage, meaning a new word).
Below is an example of how I used a nonce in Japanese Sign Language (or Japaneslan as I would like to informally call it) for the following statement I created: "My eyes are expensive [as in a sharp eye or high taste for design] but my pockets are modest." I have said this comment to a few people in written English and ASL. Then one day I came across this again in Japan and I tried to express it in "Japaneslan" or JSL. Let me introduce a few words in JSL first.
It means cheap in Japaneslan. The movement is downward.
It means expensive. The movement is upward. Many of Japaneslan words related to money have the same handshape.
As I tried to express the phrase in Japaneslan, I happened to create a new couple of nonces that the Japaneslan friends understood them and laughed. They had not seen them before but they could understand these nonces.
Nonces are the new words that are immediately created, but they might not be used again. But, if people start using them, then they would become a neoglogism.