IDIDSO

Set to 2 different clues across 2 published puzzles, most often “Emphatic confirmation of action” — The New York Times, Wednesday, 4 February 2009.

6 letters

Every clue on record, most used first

Emphatic confirmation of actiononce
The New York Times — Wednesday, 4 February 2009
Reply to "You couldn't have!"once
The New York Times — Sunday, 19 October 2008