The Collaborative International Dictionary of English v.0.48:

Indenture \In*den"ture\ (?; 135), n. [OE. endenture, OF.
   endenture, LL. indentura a deed in duplicate, with indented
   edges. See the Note below. See Indent.]
   [1913 Webster]
   1. The act of indenting, or state of being indented.
      [1913 Webster]

   2. (Law) A mutual agreement in writing between two or more
      parties, whereof each party has usually a counterpart or
      duplicate, sometimes with the edges indented for purpose
      of identification; sometimes in the pl., a short form for
      indentures of apprenticeship, the contract by which a
      youth is bound apprentice to a master.
      [1913 Webster]

            The law is the best expositor of the gospel; they
            are like a pair of indentures: they answer in every
            part.                                 --C. Leslie.
      [1913 Webster]

   Note: Indentures were originally duplicates, laid together
         and indented by a notched cut or line, or else written
         on the same piece of parchment and separated by a
         notched line so that the two papers or parchments
         corresponded to each other. But indenting has gradually
         become a mere form, and is often neglected, while the
         writings or counterparts retain the name of indentures.
         [1913 Webster]

   3. Hence: A contract by which anyone is bound to service.
      [PJC]