The Collaborative International Dictionary of English v.0.48:

Inundation \In`un*da"tion\, n. [L. inundatio: cf. F.
   inondation.]
   [1913 Webster]
   1. The act of inundating, or the state of being inundated; an
      overflow; a flood; a rising and spreading of water over
      grounds.
      [1913 Webster]

            With inundation wide the deluge reigns,
            Drowns the deep valleys, and o'erspreads the plains.
                                                  --Wilkie.
      [1913 Webster]

   2. An overspreading of any kind; overflowing or superfluous
      abundance; a flood; a great influx; as, an inundation of
      tourists.
      [1913 Webster]

            To stop the inundation of her tears.  --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inundation
    n 1: the rising of a body of water and its overflowing onto
         normally dry land; "plains fertilized by annual
         inundations" [syn: flood, inundation, deluge,
         alluvion]
    2: an overwhelming number or amount; "a flood of requests"; "a
       torrent of abuse" [syn: flood, inundation, deluge,
       torrent]

Moby Thesaurus II by Grady Ward, 1.0:

100 Moby Thesaurus words for "inundation":
   affusion, alluvion, alluvium, aspergation, aspersion, avalanche,
   baptism, bath, bathing, bedewing, burial, cataclysm, cataract,
   dampening, damping, deluge, dewing, dip, dipping, dousing,
   drowning, duck, ducking, dunking, embarras de richesses,
   engulfment, enough, exaggeration, excess, extravagance,
   extravagancy, flood, flooding, hosing, hosing down, humidification,
   immergence, immersion, irrigation, landslide, laving, lavishness,
   moistening, money to burn, more than enough, overabundance,
   overaccumulation, overbounteousness, overcopiousness, overdose,
   overflow, overflowing, overgrowth, overlavishness, overluxuriance,
   overmeasure, overmuchness, overnumerousness, overpass,
   overplentifulness, overplenty, overpopulation, overprofusion,
   overrun, overrunning, overspreading, oversufficiency, oversupply,
   plenty, plethora, pour, prodigality, redundancy, rinsing, sinking,
   souse, sousing, sparging, spate, spattering, spill, spillage,
   splashing, splattering, spraying, sprinkling, submergence,
   submersion, superabundance, superflux, superiority, surplus,
   swashing, the Deluge, the Flood, torrent, washout, watering,
   wetting, whelming