The Collaborative International Dictionary of English v.0.48:

Cheval-de-frise \Che*val"-de-frise"\, n.; commonly used in the
   pl. Chevaux-de-frise. [F.; cheval horse + Frise Friesland,
   where it was first used.] (Mil.)
   A piece of timber or an iron barrel traversed with
   iron-pointed spikes or spears, five or six feet long, used to
   defend a passage, stop a breach, or impede the advance of
   cavalry, etc.
   [1913 Webster]

         Obstructions of chain, boom, and cheval-de-frise. --W.
                                                  Irving.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cheval-de-frise
    n 1: defensive structure consisting of a movable obstacle
         composed of barbed wire or spikes attached to a wooden
         frame; used to obstruct cavalry [syn: cheval-de-frise,
         chevaux-de-frise]