Definition of "remembrancer"

I wonder, Dick, you did not put me in mind of sending for my own mattresses - But, if I had not been an ass, I should not have needed a remembrancer.

1771, Tobias Smollett, Humphry Clinker, Penguin Classics, published 1985, page 77

Tribal chieftains in Africa had had official remembrancers about them; I was Ulick's remembrancer.

1976 September, Saul Bellow, Humboldt’s Gift, New York, N.Y.: Avon Books, page 387

Near a fortnight had passed before I attempted to restrain their affliction; for premature consolation is but the remembrancer of sorrow.

1766, Oliver Goldsmith, chapter 3, in The Vicar of Wakefield