'Best man' definitions:

Definition of 'best man'

(from WordNet)
noun
The principal groomsman at a wedding

Definition of 'Best man'

From: GCIDE
  • Best \Best\ (b[e^]st), a.; superl. of Good. [AS. besta, best, contr. from betest, betst, betsta; akin to Goth. batists, OHG. pezzisto, G. best, beste, D. best, Icel. beztr, Dan. best, Sw. b[aum]st. This word has no connection in origin with good. See Better.]
  • 1. Having good qualities in the highest degree; most good, kind, desirable, suitable, etc.; most excellent; as, the best man; the best road; the best cloth; the best abilities. [1913 Webster]
  • When he is best, he is a little worse than a man. --Shak. [1913 Webster]
  • Heaven's last, best gift, my ever new delight. --Milton. [1913 Webster]
  • 2. Most advanced; most correct or complete; as, the best scholar; the best view of a subject. [1913 Webster]
  • 3. Most; largest; as, the best part of a week. [1913 Webster]
  • Best man, the only or principal groomsman at a wedding ceremony. [1913 Webster]

Definition of 'best man'

From: GCIDE
  • Groomsman \Grooms"man\, n.; pl. Groomsmen. A male attendant of a bridegroom at his wedding; -- the chief attendant is also called the best man; -- the correlative of bridesmaid. [1913 Webster]

Synonyms of 'best man'

From: Moby Thesaurus