mum-glass, n. — Green’s Dictionary of Slang

mum-glass n.

[SE mum-glass, a glass used for the drinking of mum beer, a type of beer originating in Brunswick in Germany and imported into the UK in the 17C–18C. The Monument presumably resembles such a glass]

the Monument, a 95m (311ft) column erected in 1671–77 in memory of the Great Fire of London (1666) at the junction of what is now Monument Street and Fish Street Hill.

c.1698		B.E. Dict. Canting Crew n.p.: Mum-glass, the Monument, erected at the City-charge, in Memory of the dreadful Fire 1666, which consum’d the greatest Part of it.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.