Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

brachium
     n : (biology) a branching or armlike part of an animal
     [also: {brachia} (pl)]