Synonyms for Underwater (same or very similar meaning)
WordNet sense 1 (beneath the surface of the water):
submerged, submersed
WordNet sense 2 (beneath the surface):
subsurface
WordNet sense 3 (growing or remaining under water):
subaqueous, subaquatic
WordNet sense 4 (operating or living or growing in water):
aquatic
From the ODE community, based on WordNet
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