Is it ensure, insure, or assure?
trochlea troch·le·a (trŏk'lē-ə)
n. pl. troch·le·ae (-lē-ē')
An anatomical structure that resembles a pulley, especially the part of the distal end of the humerus that articulates with the ulna.
A fibrous loop in the eye socket near the nasal process of the frontal bone, through which the tendon of the superior oblique muscle of the eye passes.