The Collaborative International Dictionary of English v.0.48:

Welter \Wel"ter\, v. i. [imp. & p. p. Weltered; p. pr. & vb.
   n. Weltering.] [Freq. of OE. walten to roll over, AS.
   wealtan; akin to LG. weltern, G. walzen to roll, to waltz,
   sich w[aum]lzen to welter, OHG. walzan to roll, Icel. velta,
   Dan. v[ae]lte, Sw. v[aum]ltra, v[aum]lta; cf. Goth. waltjan;
   probably akin to E. wallow, well, v. i. [root]146. See
   Well, v. i., and cf. Waltz.]
   [1913 Webster]
   1. To roll, as the body of an animal; to tumble about,
      especially in anything foul or defiling; to wallow.
      [1913 Webster]

            When we welter in pleasures and idleness, then we
            eat and drink with drunkards.         --Latimer.
      [1913 Webster]

            These wizards welter in wealth's waves. --Spenser.
      [1913 Webster]

            He must not float upon his watery bier
            Unwept, and welter to the parching wind,
            Without the meed of some melodious tear. --Milton.
      [1913 Webster]

            The priests at the altar . . . weltering in their
            blood.                                --Landor.
      [1913 Webster]

   2. To rise and fall, as waves; to tumble over, as billows.
      "The weltering waves." --Milton.
      [1913 Webster]

            Waves that, hardly weltering, die away.
                                                  --Wordsworth.
      [1913 Webster]

            Through this blindly weltering sea.   --Trench.
      [1913 Webster]