Economical season (including the first of April) (7)
I believe the answer is:
sparing
'economical' is the definition.
(synonyms)
'season including the first of april' is the wordplay.
'season' becomes 'spring' (spring is a season).
'including' is an insertion indicator.
'the first of april' becomes 'a' (1st letter of 'april').
'spring' enclosing 'a' is 'SPARING'.
(Other definitions for sparing that I've seen before include "Economic (with resources)" , "Thrifty" , "mean" , "Economical; having mercy" , "Moderate, economical" .)