The Collaborative International Dictionary of English v.0.48:

Manubrium \Ma*nu"bri*um\, n.; pl. L. Manubria, E.
   Manubriums. [L., handle, fr. manus hand.]
   [1913 Webster]
   1. (Anat.) A handlelike process or part; esp., the anterior
      segment of the sternum, or presternum, and the handlelike
      process of the malleus.
      [1913 Webster]

   2. (Zool.) The proboscis of a jellyfish; -- called also
      hypostoma. See Illust. of Hydromedusa.
      [1913 Webster]

WordNet (r) 3.0 (2006):

manubrium
    n 1: the upper part of the breastbone