The Collaborative International Dictionary of English v.0.48:

Brassart \Bras"sart\, n. [F. brassard, fr. bras arm. See
   Brace, n.]
   Armor for the arm; -- generally used for the whole arm from
   the shoulder to the wrist, and consisting, in the 15th and
   16th centuries, of many parts.
   [1913 Webster]