best man
US /ˌbest ˈmæn/
UK /ˌbest ˈmæn/

1.
témoin
a male friend or relative who attends the bridegroom at a wedding, and is usually his chief attendant
:
•
My brother asked me to be his best man at his wedding.
Mon frère m'a demandé d'être son témoin à son mariage.
•
The best man gave a funny speech at the reception.
Le témoin a fait un discours amusant à la réception.