Fish is rank, say (6)
I believe the answer is:
plaice
'fish' is the definition.
(plaice is a kind of fish)
'rank say' is the wordplay.
'rank' becomes 'place' (place is a kind of rank).
'say' indicates a 'sounds like' (homophone) clue.
'place' sounds like 'PLAICE'.
'is' is the link.
(Other definitions for plaice that I've seen before include "Brown flatfish" , "Edible flatfish" , "Ice, pal, will catch this fish" , "Location of the fish" , "Important food fish" .)