Rum and water. Grog was first introduced into the navy about the year 1740, by Admiral Vernon, to prevent the sailors intoxicating themselves with their allowance of rum, or spirits. Groggy, or groggified; drunk.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Groats * Grog-blossomNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes