The Collaborative International Dictionary of English v.0.48:

Fief \Fief\, n. [F. fief; of German origin, and the same word as
   E. fee. See Fee, and cf. Feud, a tief.] (Law)
   An estate held of a superior on condition of military
   service; a fee; a feud. See under Benefice, n., 2.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fief
    n 1: a piece of land held under the feudal system [syn: fief,
         feoff]