Source : Webster's Revised Unabridged Dictionary (1913)

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["a]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.

            When he is best, he is a little worse than a man.
                                                  --Shak.

            Heaven's last, best gift, my ever new delight.
                                                  --Milton.

   2. Most advanced; most correct or complete; as, the best
      scholar; the best view of a subject.

   3. Most; largest; as, the best part of a week.

   {Best man}, the only or principal groomsman at a wedding
      ceremony.

Source : WordNet®

best man
     n : the principal groomsman at a wedding