The Collaborative International Dictionary of English v.0.48:

Churn \Churn\, v. i.
   To perform the operation of churning.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Churn \Churn\ (ch[^u]rn), n. [OE. chirne, cherne, AS. ceren,
   cyrin; akin to D. karn, Dan. kierne. See Churn, v. t.]
   A vessel in which milk or cream is stirred, beaten, or
   otherwise agitated (as by a plunging or revolving dasher) in
   order to separate the oily globules from the other parts, and
   obtain butter.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Churn \Churn\, v. t. [imp. & p. p. Churned (ch[^u]rnd); p. pr.
   & vb. n. Churning.] [OE. chernen, AS. cernan; akin to LG.
   karnen, G. kernen, D. karnen, Dan. kierne, Sw. k[aum]rna, and
   also to E. corn, kernel, the meaning coming from the idea of
   extracting the kernel or marrow. See Kernel.]
   1. To stir, beat, or agitate, as milk or cream in a churn, in
      order to make butter.
      [1913 Webster]

   2. To shake or agitate with violence.
      [1913 Webster]

            Churned in his teeth, the foamy venom rose.
                                                  --Addison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

churn
    n 1: a vessel in which cream is agitated to separate butterfat
         from buttermilk [syn: churn, butter churn]
    v 1: stir (cream) vigorously in order to make butter
    2: be agitated; "the sea was churning in the storm" [syn:
       churn, boil, moil, roil]