Have weight if returning boned slice of fish (6)
I believe the answer is:
fillet
'slice of fish' is the definition.
'fillet' can be an answer for 'slice' (fillet is a kind of slice). I'm not certain of the 'of fish' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for fillet that I've seen before include "Boneless slice, of meat say" , "round head?" , "Choice piece of boneless meat (6)" , "Alice band" , "Juicy piece of boneless meat" .)