noun
- the more or less acidulous liquid remaining after butter has been separated from milk or cream.
- a similar liquid made from whole or skim milk with the addition of a bacterial culture.
noun
- the sourish liquid remaining after the butter has been separated from milk, often used for making scones and soda bread
1520s, from butter (n.) + milk (n.). Cf. German Buttermilch. It is what remains after the butter has been churned out.