best man

the chief attendant of the bridegroom at a wedding.

Origin of best man

First recorded in 1775–85

And Chandos, who acted as best-man to his old messmate, declared that it was the happiest day of his life.

The Two Shipmates |William H. G. Kingston
Being the best-man at the wedding is one of the honors that has come to Father.

Phyllis |Maria Thompson Daviess
Ann uttered a short, sudden scream of despair, and fell senseless at the feet of the best-man.

Wilson's Tales of the Borders and of Scotland, Vol. XX |Alexander Leighton
I had sent for ane o' my brothers to be best-man, and he was with me waiting when they came.

Wilson's Tales of the Borders and of Scotland Volume 18 |Alexander Leighton

It is unlucky for a bridegroom to have for his "best-man" one who is not his blood relation.

The Mysteries of All Nations |James Grant

best man

the (male) attendant of the bridegroom at a wedding