churn 
(chûrn)
(chûrn)n.
1. A vessel or device in which cream or milk is agitated to separate the oily globules from the caseous and serous parts, used to make butter.
2. Turbulence or agitation: "the violent churn of a long waterfall" (Catherine Reid).
v. churned, churn·ing, churns
v.tr.
1.
a. To agitate or stir (milk or cream) in order to make butter.
b. To make by the agitation of milk or cream: churn butter.
2. To agitate vigorously or turn over repeatedly: wind churning up the piles of leaves. See Synonyms at agitate.
3. To buy and sell (a client's securities) frequently, especially in order to generate commissions.
v.intr.
Phrasal Verb: 1. To make butter by operating a device that agitates cream or milk.
2. To be turbulent or agitated: waves churning in the storm; so angry it made my stomach churn.
3. To move by agitating water or by means of a pumping action: The boat churned through the narrows.
churn out
To produce in an abundant and regular manner: churns out four novels a year.
[Middle English chirne, from Old English cyrn, cyrin.]
churner n.