The Collaborative International Dictionary of English v.0.48:

Brachium \Brach"i*um\, n.; pl. Bracchia. [L. brachium or
   bracchium, arm.] (Anat.)
   The upper arm; the segment of the fore limb between the
   shoulder and the elbow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

brachium
    n 1: (biology) a branching or armlike part of an animal