Green’s Dictionary of Slang

1. an older, experienced and open homosexual.

1931–4		D. Clemmer Prison Community (1940) 334/1: mother superior, n. A term sometimes used in fun in connection with an elderly male homosexual, especially if popular with a number of young customers.
1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1965		Guild Dict. Homosexual Terms 31: mother superior (n.): An older, very experienced male homosexual.
1972		B. Rodgers Queens’ Vernacular.
1980		T. McClenaghan Submariners I i: Put some of that [make-up] on and we could go to the Mother Superior as a double act.
1990		(ref. to 1944) A. Bérubé Coming Out Under Fire 86: A flaming queen was a mother superior.

2. a police sergeant.

1980

Maledicta IV:2 (Winter) 230: If two patrolmen are sisters, then a sergeant is Mother Superior.