Undersea means lying or happening beneath the surface of the ocean. An undersea cable.
Nearly all the world's internet traffic runs through undersea cables rather than satellites. An undersea volcano is where most of the earth's volcanic activity actually happens.
1adjectiveunderseaLying or happening beneath the surface of the ocean, as with cables, volcanoes, and tunnels there.
“The undersea cable was cut by an anchor and took a fortnight to mend.”
undersea is a quality.
Proto-Germanic
*saiwiz
Proto-West Germanic
*saiwi — body of water
Old English
sǣ
Middle English
see
English
sea
English, today
undersea
From under- + sea. sea Middle English see, from Old English sǣ, from Proto-West Germanic saiwi (“body of water”), from Proto-Germanic saiwiz, itself either:
Etymology from Wiktionary, CC BY-SA