The Collaborative International Dictionary of English v.0.48:

Whelm \Whelm\, v. t. [imp. & p. p. Whelmed; p. pr. & vb. n.
   Whelming.] [OE. whelmen to turn over, akin to OE. whelven,
   AS. whelfan, hwylfan, in ?whylfan, ?whelfan, to overwhelm,
   cover over; akin to OS. bihwelbian, D. welven to arch, G.
   w["o]lben, OHG. welben, Icel. hvelfa to overturn; cf. Gr. ?
   bosom, a hollow, a gulf.]
   [1913 Webster]
   1. To cover with water or other fluid; to cover by immersion
      in something that envelops on all sides; to overwhelm; to
      ingulf.
      [1913 Webster]

            She is my prize, or ocean whelm them all! --Shak.
      [1913 Webster]

            The whelming billow and the faithless oar. --Gay.
      [1913 Webster]

   2. Fig.: To cover completely, as if with water; to immerse;
      to overcome; as, to whelm one in sorrows. "The whelming
      weight of crime." --J. H. Newman.
      [1913 Webster]

   3. To throw (something) over a thing so as to cover it.
      [Obs.] --Mortimer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

whelm
    v 1: overcome, as with emotions or perceptual stimuli [syn:
         overwhelm, overpower, sweep over, whelm,
         overcome, overtake]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "whelm":
   baptize, be prodigal with, blank, bulldoze, bury, cascade,
   cataract, clobber, cream, defeat utterly, deluge, dip, douse,
   drown, duck, dunk, engulf, float, flood, flood the market, flow on,
   immerge, immerse, inundate, knock over, merge, overbear, overbrim,
   overcome, overdose, overequip, overflow, overfurnish, overlavish,
   overpower, overprovender, overprovide, overprovision, overrun,
   oversell, overstock, oversupply, overwhelm, paste, plunge in water,
   pour on, pour out, pour over, prostrate, rain, run over, schmear,
   shellac, shut out, sink, skunk, slop, slosh, sluice, smear,
   snow under, souse, spill, spill out, spill over, steamroller,
   submerge, submerse, swamp, sweep, whitewash, whomp, whop