The Collaborative International Dictionary of English v.0.48:

Submerge \Sub*merge"\, v. t. [imp. & p. p. Submerged; p. pr. &
   vb. n. Submerging.] [L. submergere, submersum; sub under +
   mergere to plunge: cf. F. submerger. See Merge.]
   1. To put under water; to plunge.
      [1913 Webster]

   2. To cover or overflow with water; to inundate; to flood; to
      drown.
      [1913 Webster]

            I would thou didst,
            So half my Egypt were submerged.      --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

submerged
    adj 1: beneath the surface of the water; "submerged rocks" [syn:
           submerged, submersed, underwater]
    2: growing or remaining under water; "viewing subaqueous fauna
       from a glass-bottomed boat"; "submerged leaves" [syn:
       subaqueous, subaquatic, submerged, submersed,
       underwater]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "submerged":
   awash, bathed, behind the curtain, behind the scenes,
   between the lines, buried, camouflaged, concealed, covert, cryptic,
   debased, delitescent, deluged, depressed, dipped, disguised,
   dormant, downcast, downthrown, drenched, dribbling, dripping,
   dripping wet, drowned, engulfed, esoteric, fallen, flooded,
   hibernating, hidden, immersed, imperceptible, indiscernible,
   insensible, inundated, invisible, latent, low, lowered, lurking,
   macerated, muffled, mystic, obfuscated, obscured, occult, oozing,
   out of sight, overflowed, permeated, possible, potential,
   prostrate, reduced, saturated, secret, seeping, sightless,
   sleeping, soaked, soaking, soaking wet, soaky, sodden, soggy,
   sopping, sopping wet, soppy, soused, steeped, subaqueous,
   submarine, submersed, sunk, sunken, swamped, unapparent, unbeheld,
   unbeholdable, under the surface, underlying, undersea, underwater,
   undiscernible, unmanifested, unnoticed, unobserved, unperceivable,
   unperceived, unrealized, unseeable, unseen, unviewed, unwitnessed,
   veiled, viewless, virtual, waterlogged, watersoaked, weeping,
   weltering, whelmed, wringing wet