IFOR

Set to 2 different clues across 2 published puzzles, most often "___ one ?" (opiner's opening) — The New York Times, Friday, 23 December 2005.

4 letters

Every clue on record, most used first

"___ one ?" (opiner's opening)once
The New York Times — Friday, 23 December 2005
"___ one..." (opiner's opening)once
The New York Times — Thursday, 6 May 1999