buttermilk

UK: /ˈbʌtə^rmɪlk/ US: /ˈbʌtərˌmɪlk/ ,(but′ər milk′)

WordReference Random House Learner's Dictionary of American English © 2025

but•ter•milk /ˈbʌtərˌmɪlk/   n. [uncountable]

1. Food the liquid remaining after butter has been separated from milk or cream.

WordReference Random House Unabridged Dictionary of American English © 2025

but•ter•milk  (but′ər milk′), n. 

1. the more or less acidulous liquid remaining after butter has been separated from milk or cream.
2. Food a similar liquid made from whole or skim milk with the addition of a bacterial culture.

• butter + milk 1520–30

Collins Concise English Dictionary © HarperCollins Publishers::

buttermilk / ˈbʌtəˌmɪlk/ noun

1. the sourish liquid remaining after the butter has been separated from milk, often used for making scones and soda bread