The Collaborative International Dictionary of English v.0.48:

Arriere \Ar*riere"\, n. [F. arri[`e]re. See Arrear.]
   "That which is behind"; the rear; -- chiefly used as an
   adjective in the sense of behind, rear, subordinate.
   [1913 Webster]

   Arriere fee, Arriere fief, a fee or fief dependent on a
      superior fee, or a fee held of a feudatory.

   Arriere vassal, the vassal of a vassal.
      [1913 Webster]