For certificate see master after swim (7)
I believe the answer is:
diploma
'for certificate' is the definition.
(diploma is a kind of certificate)
'see master after swim' is the wordplay.
'see' becomes 'lo' (archaic word meaning 'look!').
'master' becomes 'ma'.
'after' is a charade indicator (letters next to each other).
'swim' becomes 'dip' (dip is a kind of swim).
'lo'+'ma'='loma'
'loma' put after 'dip' is 'DIPLOMA'.
(Other definitions for diploma that I've seen before include "Course certificate" , "Paper showing examination success" , "Certificate awarded by college for educational attainment" , "Certificate of proficiency" , "Academic certificate" .)