Grouse is grand in season (5)
I believe the answer is:
gripe
'grouse' is the definition.
(I know that grouse can be written as gripe)
'grand in season' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'in season' becomes 'ripe' (I've seen this in another clue).
'g'+'ripe'='GRIPE'
'is' acts as a link.
(Other definitions for gripe that I've seen before include "Complain; colic (water)" , "Protest" , "Complain; stomach pain" , "beef" , "Trivial complaint" .)