The Collaborative International Dictionary of English v.0.48:

Coparcener \Co*par"ce*ner\ (-n[~e]r), n. [Pref. co- + parcener.]
   (Law)
   One who has an equal portion with others of an inheritance.
   [1913 Webster]

         All the coparceners together make but one heir, and
         have but one estate among them.          --Blackstone.
   [1913 Webster]