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.]
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   1. To roll, as the body of an animal; to tumble about,
      especially in anything foul or defiling; to wallow.
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            When we welter in pleasures and idleness, then we
            eat and drink with drunkards.         --Latimer.
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            These wizards welter in wealth's waves. --Spenser.
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            He must not float upon his watery bier
            Unwept, and welter to the parching wind,
            Without the meed of some melodious tear. --Milton.
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            The priests at the altar . . . weltering in their
            blood.                                --Landor.
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   2. To rise and fall, as waves; to tumble over, as billows.
      "The weltering waves." --Milton.
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            Waves that, hardly weltering, die away.
                                                  --Wordsworth.
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            Through this blindly weltering sea.   --Trench.
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The Collaborative International Dictionary of English v.0.48:

Welter \Wel"ter\, v. t. [Cf. Wilt, v. i.]
   To wither; to wilt. [R.]
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         Weltered hearts and blighted . . . memories. --I.
                                                  Taylor.
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The Collaborative International Dictionary of English v.0.48:

Welter \Wel"ter\, a. (Horse Racing)
   Of, pertaining to, or designating, the most heavily weighted
   race in a meeting; as, a welter race; the welter stakes.
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The Collaborative International Dictionary of English v.0.48:

Welter \Wel"ter\, n.
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   1. That in which any person or thing welters, or wallows;
      filth; mire; slough.
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            The foul welter of our so-called religious or other
            controversies.                        --Carlyle.
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   2. A rising or falling, as of waves; as, the welter of the
      billows; the welter of a tempest.
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WordNet (r) 3.0 (2006):

welter
    n 1: a confused multitude of things [syn: clutter, jumble,
         muddle, fuddle, mare's nest, welter, smother]
    v 1: toss, roll, or rise and fall in an uncontrolled way; "The
         shipwrecked survivors weltered in the sea for hours"
    2: roll around, "pigs were wallowing in the mud" [syn: wallow,
       welter]
    3: be immersed in; "welter in work"