Mormon, n. — Green’s Dictionary of Slang

Mormon n.

[the polygamy performed by 19C Mormons]

(US) a promiscuous man.

1874		F. Dumont Africanus Blue Beard 11: Oh! that old villain! that old Mormon! He’s got forty wives hung up in that Blue Chamber.
1905		H. Green Actors’ Boarding House (1906) 9: Another wife! Oh, the Mormon, or if not a real one, just as bad.
1925		L. Doyle Dear Ducks 66: But I know where ye were, ye wee Mormon ye; ye were away buyin’ presents for another woman.

In compounds

Mormon candy (n.) (also Mormon currency) [the sect’s innate Puritanism eschews sweets]

(US) carrots.

1939		FWP ID Lore 241: Mormon candy — raw carrot [DARE].
1942		Berrey & Van den Bark Amer. Thes. of Sl. 474: Mormon currency; carrots [DARE].

Mormon dinner (n.)

(US) a meal that consists mainly of potatoes.

1930		‘Dean Stiff’ Milk and Honey Route 134: This is not a dish but a dinner. Some hobos call it ‘Mormon Dinner’ because the natives of Utah seem to be so fond of it. It includes boiled potatoes in their jackets.
1949		Monteleone Criminal Sl. (rev. edn).

Mormon poison (n.) [the Mormon prohibition of any beverages containing caffeine]

(US) coffee.

1984

C. Lesley Winterkill 272: ‘If there’s any leftover coffee in that thermos, bring it here. Got a corpse that needs reviving.’ ‘I can’t drink that Mormon poison until I’ve had a shot,’ Jones said. ‘You bring any whiskey?’ [DARE].

Mormon rain (n.) (also Mormon rainstorm) [the climate of Utah, the home of Mormonism]

(US) a dust storm.

1939		FWP ID Lore 241: Mormon rain — a dust storm [DARE].
c.1971		Hall Snake River Valley n.p.: (A dry storm) Mormon rainstorm [DARE].
1981		in DARE file n.p.: When a storm brings wind to stir up the dust but doesn’t produce the needed rain, it’s called a Mormon rainstorm [DARE].