buttermilk UK /ˈbʌtəˌmɪlk/US /ˈbʌtɚˌmɪlk/ noun3 •The liquid left over after producing butter from full cream milk by the churning process, also called traditional buttermilk. •Cultured buttermilk, a fermented dairy product produced from cow's milk, with a characteristically sour taste. •A light yellow color, like that of buttermilk. formsbuttermilks