1. A female ruler; a governess, a woman employed to teach and train children in a private home: Jane was hired as a rectrix, or rectoress, by a wealthy family to provide lessons for their children in science, languages, mathematics, music, and behavior.
2. The feminine administrative head of some schools, colleges, or universities: Mrs. Johnson was the principal, or rectrix, of the local educational institution in Mary’s town.
3. In ornithology, a bird’s tail feather used to guide it during flight: One of the long back quill feathers of a bird, or rectrix, is employed as a rudder or control surface, and is used to steer or to direct the path it takes while flying in the air.

The long, stiff, asymmetrically shaped feathers on the tails of a bird are called retrices and their primary functions are to aid in the production of both thrust and lift during flight.