ster·num / ˈstərnəm/ • n. (pl. -nums or -na / -nə/ ) the breastbone. ∎  Zool. a thickened ventral plate on each segment of the body of an arthropod.

sternum (breastbone)
1. A shield-shaped or rod-shaped bone in terrestrial vertebrates, on the ventral side of the thorax, that articulates with the clavicle (collar bone) of the pectoral girdle and with most of the ribs. It is absent in fish, and in birds it bears a keel.

2. The ventral portion of each segment of the exoskeleton of arthropods.

sternum
1. In tetrapods, the bone at the mid-ventral line of the thorax to which most of the ribs are attached at their ventral ends. The sternum is attached anteriorly to the pectoral girdle.

2. In Arthropoda, a ventral cuticle on each segment that forms a thickened plate. See STERNITE.

sternum (ster-nŭm) n. (pl. sterna) the breastbone: a flat bone extending from the base of the neck to just below the diaphragm and forming the front part of the skeleton of the thorax. The sternum articulates with the collar bones (see clavicle) and the costal cartilages of the first seven pairs of ribs.
—sternal adj.

sternum (breastbone) Flat, narrow bone extending from the base of the front of the neck to just below the diaphragm in the centre of the chest. The top attaches by ligaments to the collarbones and the centre part joins to the ribs by seven pairs of costal cartilages.