Sternum is a word that can be traced back to a couple of Greek terms for breast: sternon, a poetic designation for the breast of a man (but not that of a woman) and stethos, an anatomical term for either the breast of a man or woman (and from which comes stethoscope).
Galen, in second century Rome, was the first to use sternon in the anatomical sense of breast bone; the word transformed into sternum sometime after the fall of the Roman empire in the 6th century. However, os pectoris was the preferred Latin term for well over 1500 years, from the time of ancient Rome through the Renaissance, and was used by Vesalius in the Fabrica. Sternum didn't show up in English until the 17th century and os pectoris was still appearing in English medical dictionaries late into the 19th century.
The components of the sternum are rich in sword-related etymologies. See manubrium for details.
The bone exhibits a little-known sexual dimorphism: in males the body is typically more than twice the length of the manubrium; in females it is usually less than twice the length. It also shows a number of common structural variations.
Variations in sternum structure.
From The Illustrated Encyclopedia of Human Anatomic Variation. In a 2006 study done in Istanbul, Turkey, X-ray examination of 1000 individuals with otherwise normal sternums showed 4% with suprasternal bones, 4.5% with a foramen in the body, 27% with a xiphoid foramen, and 27% with a bifid xiphoid process.