The Collaborative International Dictionary of English v.0.48:

Selectman \Se*lect"man\, n.; pl. Selectmen.
   One of a board of town officers chosen annually in the New
   England States to transact the general public business of the
   town, and have a kind of executive authority. The number is
   usually from three to seven in each town.
   [1913 Webster]

         The system of delegated town action was then, perhaps,
         the same which was defined in an "order made in 1635 by
         the inhabitants of Charlestown at a full meeting for
         the government of the town, by selectmen;" the name
         presently extended throughout New England to municipal
         governors.                               --Palfrey.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

SELECTMEN. The name of certain officers in several of the United States, who
are invested by the statutes of the several states with various powers.