undersea
UK: ˌʌndəˈsiː | US: ˌʌndərˈsiː
adj. located, occurring, or existing beneath the surface of the sea
n. the region or environment beneath the surface of the sea
The word "undersea" is a straightforward compound of "under" (from Old English under, meaning "beneath") and "sea" (from Old English sǣ, meaning "large body of water"). It emerged in the early 19th century to describe anything situated or occurring below the ocean's surface. The logical combination reflects the physical relationship between the prefix and root, making it easy to decode and remember.
The undersea cable connects continents for high-speed internet.
Scientists discovered an undersea volcano near the coast.
The documentary explores undersea life in the Mariana Trench.
Divers use special equipment to withstand undersea pressure.
Coral reefs are vital to undersea ecosystems.