Definition of pectoralis in US English:

pectoralis

noun

Anatomy Zoology
  • Any of the major pectoral muscles in tetrapods; specifically = pectoralis major.

Origin

Early 17th century; earliest use found in Helkiah Crooke (1576–1648), physician and anatomist. From post-classical Latin pectoralis, use as noun (short for pectoralis musculus) of classical Latin pectorālis, adjective.