supinator

su·pi·na·tor

noun \ˈsü-pə-ˌnāt-ər\

Definition of SUPINATOR

: a muscle that produces the motion of supination; specifically : a deeply situated muscle of the forearm that arises in two layers from the lateral epicondyle of the humerus and adjacent parts of the ligaments and bones of the elbow and that passes over the head of the radius to insert into its neck and the lateral surface of its shaft