Green’s Dictionary of Slang

forenoon n.

an alcoholic drink taken before breakfast.

[Aus]Mercury (Hobart) 23 Apr. 2/5: [from the Stranraer Free Press] [...] a mornin’, a forenoon, a nightcap.
[UK]‘William Juniper’ True Drunkard’s Delight 228: You may have a [...] forenoon.