Man has fish to be polite (7)
I believe the answer is:
genteel
'be polite' is the definition.
(synonyms)
'man has fish' is the wordplay.
'man' becomes 'gent' (gent is a kind of man).
'has' means one lot of letters go next to another.
'fish' becomes 'eel' (eel is a type of fish).
'gent'+'eel'='GENTEEL'
'to' is the link.
(Other definitions for genteel that I've seen before include "Courtly, cultivated" , "Marked by refinement in taste and manners" , "Mannerly" , "Well mannered" , "Artificially polite" .)