Green’s Dictionary of Slang

1. a coffin, thus overcoat tailor, a coffin-maker.

1898		Binstead & Wells A Pink ’Un and a Pelican 257: Leo’s last overcoat [...] commenced with a zinc shell, over which were three layers of walnut, another zinc interlining, and, outside all, a chestnut casket, five inches thick.
1917		W. Thorin letter 28 Jan. in Weeks (ed.) Greater Love Hath No Man (1939) 195: I am getting on pretty fair and if I don’t get into another mess I might cheat the overcoat tailor yet.
1934		C.S. Johnson Shadow of the Plantation 39: I plum’ out of all the ’cieties now. [...] I’ll have to join some others ‘cause my overcoat [coffin] cost too much’.
1941		V. Davis Phenomena in Crime 167: The boys will pay for an overcoat (coffin) from the best makers.
2007		S. Maloney Sucked In 8: Charlie was the quiet one in the rosewood overcoat.

2. (US) a pie crust.

1940

(con. 1914) S.J. Simonsen Soldier Bill 11: ‘Hash with overcoats,’ meant meat balls with pie crust around them.

3. (also Dunlop overcoat) a condom.

1938		‘Justinian’ Americana Sexualis 30: Overcoat. n. A cundum.
1972		B. Rodgers Queens’ Vernacular.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 9: It seemed like no time at all that her Onkarparingas had slipped a Dunlop overcoat on his eight-day-clock and the contract had been fulfilled.

4. (US) a high value currency note around a bankroll.

1935

A.J. Pollock Und. Speaks.

5. (US) a straitjacket.

1935

A.J. Pollock Und. Speaks.

6. (US) a parachute.

1942

Berrey & Van den Bark Amer. Thes. Sl.