Green’s Dictionary of Slang

(US) rotgut whisky.

1841		A.M. Maxwell Run Through the United States I 157: They adroitly turned the tables upon their opponents by making Ohio buck-eye, hard cider, and log-huts.
1851		‘Bingo’ in T.A. Burke Polly Peablossom’s Wedding 61: The liquor was called for – a pint of buck-eye whiskey.
1878		in M. Lewis Mining Frontier (1967) 72: I went to work and made up a decoction of poison oak and buckeye.
1954		Harder Collection n.p.: Buck-eye whiskey: ‘Buck-eye poison give you the jake leg’ [DARE].
1966		in DARE.
1974		J.E. Dabney Mountain Spirits 24: ‘Buckeye bark whiskey’ got its name from the fact that moonshiners put buckeyes (inedible nuts that grow in the hills) into the newly-run liquor – to give it a bourbon red color.