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undersea

American  
[uhn-der-see] / ˈʌn dərˌsi /

adjective

  1. located, carried on, or used under the surface of the sea.

    undersea life.

adverb

  1. underseas.

undersea British  
/ ˈʌndəˌsiː /

adjective

  1. below the surface of the sea

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of undersea

First recorded in 1605–15; under- + sea

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

A significant share of global web traffic passes through the Strait via undersea cables, largely servicing countries in the Gulf and South Asia.

From Barron's • Apr. 12, 2026

Healey warned Russia of “serious consequences” for future damage, amid broader Western concerns about Russian and Chinese undersea activity.

From The Wall Street Journal • Apr. 9, 2026

The UK is dependent on its undersea cables and pipelines for its data and energy.

From BBC • Apr. 9, 2026

Those submarines were discovered over critical assets like undersea pipelines.

From The Wall Street Journal • Apr. 9, 2026

A dim, undersea light filtered through the slits of the cellar windows.

From "The Bell Jar" by Sylvia Plath

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.