Green’s Dictionary of Slang

(US) money.

1885		McCook Trib. (NE) 8 Oct. 2/1: He [an Italian] also claimed to be a stranger in the city [...] and had plenty ‘o’ de mon’.
1888		A. Trumble Mott Street Poker Club 42: ‘Havee plenty mon [...] Havee too muchee mon’.
1893		S. Crane Maggie, a Girl of the Streets (2001) 64: Put yer mon in yer pocket! Yer loaded an’ yehs on’y makes a damn fool of yerself.
1894		Mirror of Life 17 Feb. 3/3: The enraged Italian grasped the ‘monk’ by the throat, shouting, ‘Giva da mon I Give da mon’.
1896		W.C. Gore Student Sl. in Cohen (1997) 7: mun n. Money.
1913		Nebraska State Journal 8 Dec. in DN IV:ii 120: No hold-up man who draws his gun on me will ever get my mon.
1913		Sport (Adelaide) 23 Aug. 9/3: Archie H is on the run, / Catching tarts with ‘you’re the one,’ / I know he has taken them to the Pav, / Now where on earth did he get the mon?
1917		R. Lardner ‘The Water Cure’ in Gullible’s Travels 192: I don’t have to work [...] I got the mon.
1924		F.J. Wilstach Sl. Dict. Stage 29: ‘Mazum,’ ‘mazuma,’ ‘cush,’ ‘denoya,’ ‘rocks,’ ‘spons,’ ‘spondulix,’ ‘long green,’ ‘yellowbacks,’ ‘dough,’ ‘mononny,’ ‘da mon’.
1930		J. Byrd ‘Old Timbrook Blues’ 🎵 Old Missus went to the race track and lost all-a her mon.
1952		H. Williams ‘Jambalaya’ 🎵 Swap my mon to buy Yvonne what she need-o.
1972		E. Sanders Family 181: Wilder, whose attitude was ‘Where’s the mon?’ [...] was worried lest Charlie should burn him for the session money.