In court, long for prestige (6)
I believe the answer is:
cachet
'prestige' is the definition.
('cachet' can be a synonym of 'prestige')
'in court long' is the wordplay.
'in' means one lot of letters goes inside another.
'court' becomes 'ct'.
'long' becomes 'ache' ('ache' can be a synonym of 'long').
'ct' placed around 'ache' is 'CACHET'.
'for' is the link.
(Other definitions for cachet that I've seen before include "Official seal - prestige" , "Mark of approval" , "Distinctive stamp" , "Seal; mark of prestige" , "French prestige or distinguishing mark" .)