Economical season (including the first of April) (7)
I believe the answer is:
sparing
'economical' is the definition.
(I know that economical can be written as sparing)
'season including the first of april' is the wordplay.
'season' becomes 'spring' (spring is a season).
'including' means one lot of letters goes inside another.
'the first of april' becomes 'a' (first letter of the word 'April').
'spring' placed around 'a' is 'SPARING'.
(Other definitions for sparing that I've seen before include "Economic (with resources)" , "Thrifty" , "mean" , "Economical; having mercy" , "Moderate, economical" .)