NOOP

Set to 3 different clues across 4 published puzzles, most often “Informal denial” — The New York Times, Saturday, 16 December 2006.

4 letters

Every clue on record, most used first

Informal denial2 times
The New York Times — Saturday, 16 December 2006
Colloquial denialonce
The New York Times — Saturday, 11 June 2005
"Are you nervous?" response, a la Don Knottsonce
The New York Times — Sunday, 20 July 1997