The Collaborative International Dictionary of English v.0.48:

Submersion \Sub*mer"sion\, n. [L. submersio: cf. F. submersion.]
   1. The act of submerging, or putting under water or other
      fluid, or of causing to be overflowed; the act of plunging
      under water, or of drowning.
      [1913 Webster]

   2. The state of being put under water or other fluid, or of
      being overflowed or drowned.
      [1913 Webster]

WordNet (r) 3.0 (2006):

submersion
    n 1: sinking until covered completely with water [syn:
         submergence, submerging, submersion, immersion]
    2: the act of wetting something by submerging it [syn:
       submersion, immersion, ducking, dousing]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "submersion":
   absorbed attention, absorption, affusion, alluvion, alluvium,
   application, aspergation, aspersion, baptism, bath, bathing,
   bedewing, burial, cataclysm, concentration, contemplation,
   dampening, damping, deep study, deep thought, deluge, dewing, dip,
   dipping, displacement, dousing, draft, drowning, duck, ducking,
   dunking, engagement, engrossment, engulfment, flood, flooding,
   hosing, hosing down, humidification, immergence, immersion,
   intentness, inundation, involvement, irrigation, laving,
   meditation, moistening, monomania, obsession, overflow,
   overflowing, overrunning, preoccupation, profound thought,
   rapt attention, rinsing, single-mindedness, sinkage, sinking,
   souse, sousing, sparging, spattering, spill, spillage, splashing,
   splattering, spraying, sprinkling, studiousness, study,
   submergence, swashing, the Deluge, the Flood, washout, watering,
   wetting, whelming