Definition of "monitress"

Diana filled up all his heart: he felt as if by his union with her he had received a new and better soul. She was his monitress as he learned what were the true ends of life.

1820, Mary Shelley, Mathilda, published 1959

Maisie could feel his monitress stiffen almost with anguish against the increase of his spell and then hurl herself as a desperate defence from it into the quite confessed poorness of violence, of iteration.

1897, Henry James, What Maisie Knew

Miss Mitchell would certainly be most relieved to have a monitress who was capable of organising the juniors at games.

1922, Angela Brazil, Monitress Merle