Definition of peroneus tertius in US English:

peroneus tertius

(also peronaeus tertius)

noun

Anatomy Zoology
  • A small muscle of the leg, sometimes absent, that arises from the fibula, inserts on to the fifth metatarsal bone, and acts to dorsiflex and evert the foot.

Origin

Mid 18th century. From post-classical Latin peroneus tertius from peroneus + classical Latin tertius third.