ODO

Set to 7 different clues across 20 published puzzles, most often “Prefix with meter” — The New York Times, Tuesday, 3 May 2011.

3 letters

Every clue on record, most used first

Prefix with meter14 times
The New York Times — Tuesday, 3 May 2011
"Deep Space Nine" roleonce
The New York Times — Thursday, 5 May 2011
Pope Urban II, originallyonce
The New York Times — Sunday, 25 June 2000
"Star Trek: D.S.9" characteronce
The New York Times — Sunday, 23 August 1998
"Deep Space Nine" changelingonce
The New York Times — Sunday, 28 January 1996
"_____ you know the muffin man" (children's lyric)once
The New York Times — Sunday, 3 July 1994
"Deep Space Nine" characteronce
The New York Times — Friday, 11 February 1994