clāvīcula

Clāvīcula is the diminutive of Latin clāvis (key). The collarbone was named for its resemblance to an ancient Roman key — not a modern key but the long, thin, S-curved keys used to operate Roman locks. When the arm is raised, the clavicle rotates on its long axis. The motion mimics the turning of a key. The anatomist who named it — possibly Celsus, writing in the 1st century CE — saw a key where we see a bone.

The clavicle is the most commonly broken bone in the human body. It is thin, exposed, and positioned where impacts land — falls on outstretched hands, tackles in rugby, bicycle crashes. Clavicle fractures have been documented in medical texts since Hippocrates. The Hippocratic Corpus, from the 5th–4th centuries BCE, describes treatment by binding the arm to the body with bandages. The treatment has not fundamentally changed in 2,400 years.

Anatomically, the clavicle is a bridge. It is the only bony connection between the arm and the trunk. Without it, the scapula would float free, and the shoulder would collapse inward. The word clāvīcula — little key — is more accurate than its coiner knew. The clavicle locks the shoulder in position. It is a key. It locks something.

English adopted clavicle from French in the 17th century. The English alternative — collarbone — is a Germanic compound that names the bone by its location (at the collar) rather than its shape or function. Collarbone in the gym, clavicle in the clinic. The Latin word won in medicine because Latin won in medicine.