Meat from grouse or carp (4)
I believe the answer is:
beef
'meat' is the definition.
(beef is a kind of meat)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for beef that I've seen before include "Type of meat" , "Grumble - muscle" , "Bovine flesh" , "Grumble over cattle meat?" , "Complaint; strength" .)