Top marks repeated in match (6)
I believe the answer is:
summit
'top' is the definition.
('summit' can be a synonym of 'top')
'marks repeated in match' is the wordplay.
'marks' becomes 'm' (former German currency).
'repeated' indicates the doubling of some letters.
'in' means one lot of letters goes inside another.
'match' becomes 'suit' (suiting is a kind of matching**).
'm' doubled is 'mm'.
'mm' inserted into 'suit' is 'SUMMIT'.
(Other definitions for summit that I've seen before include "Top or extreme point" , "Talks" , "Apex" , "The highest peak" , "Peak or crest" .)