Smarten up a man on his wedding day (5)
I believe the answer is:
groom
'smarten' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for groom that I've seen before include "school" , "Horse carer" , "Man in stable (about to be married?)" , "man of the match" , "Prepare; one getting wed" .)