nonce word

:  a word (as ringday in “four girls I know have become engaged today: this must be ringday”) coined and used apparently to suit one particular occasion sometimes independently by different writers or speakers but not adopted into use generally Coleridge coined mammonolatry in 1820 as a nonce word I still think I heard it, though so seldom that it had more or less the air of a nonce word — S. T. Byington