underwater

Short definition from Wiktionary

Adjective

1. 1
   Beneath the surface of the water; of or pertaining to the region beneath the water surface.
2. 2
   Beneath the water line of a vessel.
3. 3
   In difficulty, especially financially.
4. 4
   Having negative equity; owing more on an asset than its market value.
5. 5
   Of an option, having a strike price higher (call options) or lower (put options) than the current market price of the underlying asset or financial product; for example, an option to buy shares at $20 when the current market price is $15.

Adverb

1. 1
   So as to go beneath the surface of the water.

Noun

1. 1
   Underlying water or body of water, for example in an aquifer or the deep ocean.
2. 2
   A type of lure which lies beneath the water surface.

Verb

1. 1
   To water or irrigate insufficiently.