What is a small cartilaginous process of the lower part of the breastbone called?

The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous process (extension) of the lower (inferior) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. The names derived both from the Greek "xiphoid" and its Latin equivalent "ensiform" mean 'swordlike'.

In newborns and young (especially slender) infants, the tip of the xiphoid process may be both seen and felt as a lump just below the sternal notch. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major joints, this is non-movable. Ossification of the xiphoid process occurs around age 40.