Source : Webster's Revised Unabridged Dictionary (1913)

Frankpledge \Frank"pledge`\, n. [Frank free + pledge.] (O. Eng.
   Law)
   (a) A pledge or surety for the good behavior of freemen, --
       each freeman who was a member of an ancient decennary,
       tithing, or friborg, in England, being a pledge for the
       good conduct of the others, for the preservation of the
       public peace; a free surety.
   (b) The tithing itself. --Bouvier.

             The servants of the crown were not, as now, bound
             in frankpledge for each other.       --Macaulay.