Bridegroom's attendant (4,3)
I believe the answer is:
best man
'bridegroom's attendant' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for best man that I've seen before include "The groom's right-hand supporter" , "The groom's assistant at a wedding" , "Key union facilitator r" , "Important supporting role at a wedding" , "Groom's friend" .)