From The Collaborative International Dictionary of English v.0.48:
Sternum \Ster"num\, n.; pl. L. Sterna, E. Sternums. [NL.,
from Gr. ?, the breast, chest.]
1. (Anat.) A plate of cartilage, or a series of bony or
cartilaginous plates or segments, in the median line of
the pectoral skeleton of most vertebrates above fishes;
the breastbone.
[1913 Webster]
Note: The sternum is connected with the ribs or the pectorial
girdle, or with both. In man it is a flat bone, broad
anteriorly, narrowed behind, and connected with the
clavicles and the cartilages of the seven anterior
pairs of ribs. In most birds it has a high median keel
for the attachment of the muscles of the wings.
[1913 Webster]
2. (Zool.) The ventral part of any one of the somites of an
arthropod.
[1913 Webster]