The Collaborative International Dictionary of English v.0.48:

Purparty \Pur"par`ty\, n. [OF. pourpartie; pour for + partie a
   part; cf. OF. purpart a respective part.] (Law)
   A share, part, or portion of an estate allotted to a
   coparcener. [Written also purpart, and pourparty.]
   [1913 Webster]

         I am forced to eat all the game of your purparties, as
         well as my own thirds.                   --Walpole.
   [1913 Webster]

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

PURPARTY. That part of an estate, which having been held in common by
parceners, is by partition allotted to any of them. To make purparty is to
divide and sever the lands which fall to parceners. Old Nat. Br. 11.