The Collaborative International Dictionary of English v.0.48:

Vambrace \Vam"brace\, n. [See Vantbrass.] (Anc. Armor)
   The piece designed to protect the arm from the elbow to the
   wrist.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vambrace
    n 1: cannon of plate armor protecting the forearm [syn:
         vambrace, lower cannon]