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.
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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.
      [1913 Webster]

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"

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "welter":
   arsy-varsiness, bask, bend, blunder, careen, career, clutter,
   cower, cringe, crouch, falter, farrago, flounce, flounder,
   get down, grovel, hash, heave, helter-skelter, higgledy-piggledy,
   hobbyhorse, hodgepodge, hunch, hunch down, hysteron proteron,
   indulge, jumble, labor, litter, lurch, luxuriate,
   make heavy weather, mess, mishmash, mummify, mummy, pitch,
   pitch and plunge, pitch and toss, plunge, pound, rear, reel, revel,
   rock, roll, rollick, scend, scramble, scrouch down, seethe,
   shrivel, squat, stagger, stoop, strive, struggle, stumble, sway,
   swing, thrash about, topsy-turviness, topsy-turvydom, toss,
   toss and tumble, toss and turn, totter, tumble, turmoil,
   unholy mess, volutation, wallop, wallow, wilt, wizen, writhe,
   yaw