Fourth month (5)
I believe the answer is:
april
'fourth 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 "''... is the cruellest month'' (TS Eliot)" , "Month that's autumnal in Oz" , "March is followed by this" , "4th month" , "Start of the financial year" .)