EARTHDAY

Set to 2 different clues across 2 published puzzles, most often “Environmentalists' celebration” — The New York Times, Monday, 20 December 2004.

8 letters

Every clue on record, most used first

Environmentalists' celebrationonce
The New York Times — Monday, 20 December 2004
April celebrationonce
The New York Times — Wednesday, 21 January 1998