A season outside is frugal (7)
I believe the answer is:
sparing
'frugal' is the definition.
('sparing' can be a synonym of 'frugal')
'a season outside' is the wordplay.
I cannot really understand how this works, but
'a' is within the answer.
'season' could be 'spring' (spring is a kind of season) and 'spring' is present in the remaining letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for sparing that I've seen before include "Scanty - merciful" , "Moderate, economical" , "mean" , "Economic (with resources)" , "Economical; having mercy" .)