Green’s Dictionary of Slang

a half-quartern loaf.

1873		Sl. Dict. 141: Dead man, a baker. Properly speaking, it is an extra loaf smuggled into the basket by the man who carries it out, to the loss of the master. Sometimes the dead man is charged to a customer, though never delivered. Among London thieves and low people generally a ‘dead’un’ is a half-quartern loaf.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1890–1904		Farmer & Henley Sl. and Its Analogues.