Proper male swimmer (7)
I believe the answer is:
genteel
'proper' is the definition.
(thesaurus)
'male swimmer' is the wordplay.
'male' becomes 'gent' (gent is a kind of male).
'swimmer' becomes 'eel' (eel is a kind of fish).
'gent'+'eel'='GENTEEL'
(Other definitions for genteel that I've seen before include "Exaggeratedly polite" , "Courtly, cultivated" , "Refined in taste and manners" , "Mannerly" , "Courteous, well-bred" .)