The Collaborative International Dictionary of English v.0.48:

Friborg \Fri"borg\, Friborgh \Fri"borgh\, n. [AS. fri[eth]borh,
   lit., peace pledge; fri[eth] peace + borh, borg, pledge, akin
   to E. borrow. The first part of the word was confused with
   free, the last part, with borough.] (Old Eng. Law)
   The pledge and tithing, afterwards called by the Normans
   frankpledge. See Frankpledge. [Written also friburgh
   and fribourg.] --Burril.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
       [1913 Webster]

             The servants of the crown were not, as now, bound
             in frankpledge for each other.       --Macaulay.
       [1913 Webster]