Meaning

noun residue from making butter from sour raw milk; or pasteurized milk curdled by adding a culture

originInherited from Middle English butter-melke, equivalent to butter + milk. Cognate with Dutch botermelk (“buttermilk”), German Buttermilch (“buttermilk”), Low German Bottermelk (“buttermilk”), Luxembourgish Bottermëllech (“buttermilk”), Plautdietsch Bottamalkj, Bottamaltj, Bottermalkj, Bottermaltj (“buttermilk”), and Yiddish פּוטערמילך (putermilkh), פּוטער־מילעך (puter-milekh, “buttermilk”).

Etymology from Wiktionary, CC BY-SA 3.0