Rook with flatfish brings comfort when distressed (7)
I believe the answer is:
console
'comfort when distressed' is the definition.
(as in consoling a distressed person)
'rook with flatfish' is the wordplay.
'rook' becomes 'con' (synonyms).
'with' means one lot of letters go next to another.
'flatfish' becomes 'sole' (sole is a kind of flatfish).
'con'+'sole'='CONSOLE'
'brings' acts as a link.
(Other definitions for console that I've seen before include "Cheer in distress" , "Give moral or emotional strength to" , "Key-desk of an organ" , "Computer games machine" , "Instrument panel" .)