subsea

adjective

sub·​sea ˌsəb-ˈsē 

variants or less commonly sub-sea

1

: existing or occurring below the surface of the sea

subsea currents

The island, an upthrust of volcanic rock, lies along the Norfolk Ridge, an 1,100-mile line of subsea mountains.

—Michael Davie

2

: existing or occurring under the seafloor

subsea oil wells

Word History

First Known Use

1817, in the meaning defined at sense 1