Meaning of “churn” - Learner’s Dictionary

churn

verb uk us /tʃɜːn/
SURFACE [ T ] ( also churn up)

to mix something, especially liquids, with great force:

The sea was churned up by heavy winds.
STOMACH [ I ]

If your stomach is churning, you have a slight feeling that you are going to vomit, usually because you are nervous.

BUTTER [ T ]

to mix milk until it becomes butter

(Definition of “churn verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)