Filed from 6 published puzzles

COOLASACUCUMBER

Set to 6 different clues across 6 published puzzles, most often “Unlikely to crack” — The New York Times, Friday, 5 April 2002.

15 letters

Every clue on record, most used first

Unlikely to crackonce
The New York Times — Friday, 5 April 2002
Composedonce
The New York Times — Friday, 2 January 1998
...vegetable...once
The New York Times — Monday, 16 December 1996
Imperturbableonce
The New York Times — Wednesday, 28 February 1996
Really calmonce
The New York Times — Wednesday, 14 December 1994
Completely unperturbedonce
The New York Times — Tuesday, 28 December 1993

Other answers to these clues

COOL4 letters
EVEN4 letters
SEDATE6 letters
SERENE6 letters
STAID5 letters
TYPESET7 letters
WROTE5 letters