Rainy month (5)
I believe the answer is:
april
'rainy 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 "4th month" , "whose first date is foolish?" , "''... is the cruellest month''(Elliot)" , "Calendar month" , "Spring month" .)