Polish off cod, say, outside home (6)
I believe the answer is:
finish
'polish off' is the definition.
(I've seen this before)
'cod say outside home' is the wordplay.
'cod say' becomes 'fish' (cod is a kind of fish).
'outside' indicates putting letters inside.
'home' becomes 'in' ('he's home' can mean 'he's in').
'fish' going around 'in' is 'FINISH'.
(Other definitions for finish that I've seen before include "curtains" , "Complete or terminate" , "End, conclusion" , "Conclude, wind up" , "Refinement in social graces" .)