- existing or occurring under water.
- designed to be used under water.
- located below a ship’s waterline.
- beneath the water: to travel underwater.
- the water beneath the surface: cold currents in the underwater.
- underwaters, the depths, as of a sea, lake, etc.
- being, occurring, or going under the surface of the water, esp the seaunderwater exploration
- nautical below the water line of a vessel
- (of a stock option or other asset) having a market value below its purchase value
- beneath the surface of the water
adj.1620s, from under + water (n.). Of mortgages from 2008.