Tax deadline month (5)
I believe the answer is:
april
'tax deadline 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 "days on end" , "'All in an ... evening' (Katharine Tynan)" , "''... is the cruellest month'' (TS Eliot)" , "First month of the year with 30 days" , "TS Eliot's 'cruelest month'" .)