The term 'breastbone pertaining to' can be answered by two crossword solutions: 'sternal' and 'STERNUM'. The sternal bone, also known as the breastbone, is a flat bone located in the center of the chest. It connects to the ribs on either side and forms the front of the rib cage. The STERNUM is the medical term for the sternal bone. It is an important part of the human body, providing protection for the heart and lungs.