The Collaborative International Dictionary of English v.0.48:

Tidal wave \Tid"al wave\, n.
   1. an unusually high wave from the sea, sometimes reaching
      far inland and causing great destruction, and usually
      caused by some event, such as an earthquake, far from the
      shore. In Japan, such a wave is called a tsunami.
      [PJC]

   2. [fig.] an unusually large quantity of items or events
      requiring attention and causing strain on the capacity to
      handle them; as, a tidal wave of orders for a new product;
      a tidal wave of tourists.
      [PJC]

WordNet (r) 3.0 (2006):

tsunami
    n 1: a cataclysm resulting from a destructive sea wave caused by
         an earthquake or volcanic eruption; "a colossal tsunami
         destroyed the Minoan civilization in minutes"

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "tsunami":
   apoplexy, billow, bore, breakers, breakup, cataclysm, chop,
   choppiness, chopping sea, climax, comb, comber, convulsion,
   diastrophism, dirty water, disaster, eagre, fit, gravity wave,
   ground swell, heave, heavy sea, heavy swell, lift, lop, overthrow,
   paroxysm, peak, popple, quake, riffle, ripple, rise, roll, roller,
   rough water, scend, sea, send, spasm, stroke, surf, surge, swell,
   temblor, tidal bore, tidal wave, tide wave, trough, undulation,
   upheaval, water wave, wave, wavelet, white horses, whitecaps