Filed from 2 published puzzles

ATONALITY

Set to 2 different clues across 2 published puzzles, most often “Feature of the 1925 opera "Wozzeck"” — The New York Times, Saturday, 11 April 2009.

9 letters

Every clue on record, most used first

Feature of the 1925 opera "Wozzeck"once
The New York Times — Saturday, 11 April 2009
Quality of Bartók's musiconce
The New York Times — Saturday, 9 July 2005