Filed from 2 published puzzles

WACKY

Set to 2 different clues across 2 published puzzles, most often “Screwball” — The New York Times, Wednesday, 13 October 2004.

5 letters

Every clue on record, most used first

Screwballonce
The New York Times — Wednesday, 13 October 2004
Amusingly eccentriconce
The New York Times — Wednesday, 20 August 2003

Other answers to these clues

KOOK4 letters
KOOKY5 letters
LOON4 letters
NUT3 letters
NUTCASE7 letters
SENSELESS9 letters
ZANY4 letters