underwater

adjective

1. existing or occurring under water.
2. designed to be used under water.
3. located below a ship’s waterline.

adverb

4. beneath the water: to travel underwater.

noun

5. the water beneath the surface: cold currents in the underwater.
6. underwaters, the depths, as of a sea, lake, etc.

adjective

1. being, occurring, or going under the surface of the water, esp the seaunderwater exploration
2. nautical below the water line of a vessel
3. (of a stock option or other asset) having a market value below its purchase value

adverb

4. beneath the surface of the water

adj.1620s, from under + water (n.). Of mortgages from 2008.