underwater

adjective

un·​der·​wa·​ter ˌən-dər-ˈwȯ-tər 

-ˈwä-

1

: lying, growing, worn, performed, or operating below the surface of the water

underwater plants

2

: being below the waterline of a ship

3

a

: having, relating to, or being a mortgage loan for which more is owed than the property securing the loan is worth

homeowners who are underwater on their loans

b

: having, relating to, or being a stock option for which the price of the option is higher than the current market value of the stock

underwater adverb

Synonyms of underwater

• aquatic
• submarine
• submerged

Examples of underwater in a Sentence

underwater plants don't require as much light to grow as surface plants

a vessel designed for underwater exploration

Recent Examples on the Web

However, Microsoft ended the project in 2024 and chose not to build more underwater data centers. — Nir Kshetri, The Conversation, 17 Aug. 2026

The vessel supports the testing and deployment of robotic and autonomous, crewed and uncrewed underwater systems, and undersea surveillance systems, according to a press release. — Prabhat Ranjan Mishra, Interesting Engineering, 16 Aug. 2026

Downtown Redwood City’s newest Art Kiosk installation takes a look at what happens when an entire underwater ecosystem disappears where most people will never see it. — Anne Gelhaus, Mercury News, 16 Aug. 2026

For the past year, University of Washington researchers have worked closely with the Samish Indian Nation to bring this 24-armed creature back from the brink of extinction after a vast underwater pandemic nearly wiped it out. — John Ryan, NPR, 16 Aug. 2026

Word History

First Known Use

1627, in the meaning defined at sense 1

Rhymes for underwater

• imprimatur
• auteur
• blotter
• cotter
• daughter
• hotter
• mater
• otter
• plotter
• rotter
• slaughter
• spotter

Kids Definition

underwater

adjective

un·​der·​wa·​ter ˈən-dər-ˈwȯt-ər 

-ˈwät-

: lying, growing, worn, performed, or operating below the surface of the water

underwater plants

an underwater cave

underwater

-ˈwȯt-, 

-ˈwät-

adverb

Legal Definition

underwater

adjective

un·​der·​wa·​ter

1

: owing more on a mortgage loan than the property securing the loan is worth

underwater homeowners

2

: being or relating to a mortgage loan in which more is owed than the property securing the loan is worth

underwater mortgages

underwater properties