From Longman Dictionary of Contemporary Englishbest manˌbest ˈman noun [singular] MARRYthe man who helps the bridegroom at a wedding ceremony
Examples from the Corpus
best man• And her frail brother bravely struggled from his sick bed to be best man.• They were close friends, and Critchley was the best man at Heseltine's wedding.• The bride walked to the church with the best man with the groom following. 