Earth Day's month (5)
I believe the answer is:
april
'earth day's month' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for april that I've seen before include "Start of the second quarter" , "Month of showers and of the Queen's birthday" , "The month with All Fools' Day" , "''All in an ... evening / ... airs were abroad'' (by Katherine Tynan)" , "Traditionally showery month" .)