undersea

adj

1. (not-comparable)Existing, relating to, or made for use beneath the sea.

   “It is not known just what action will be taken against the captain of the undersea boat.”

   “"You're right!" she cried. "I'm sure you are." Twenty reasons come back. An undersea tunnel to the little island.”

   “The Sediment (SNAP-7E) Density Meter (an underwater rocket) has been developed to investigate to an ocean-bottom depth of 11 sedimentary feet. Sea Lab I, the Navy’s new undersea laboratory, complete with observation porch and garage, should become safe to operate at the 200 foot level.”

   “The bull kelp forests off Northern California are sometimes spoken of as the redwoods of the sea. And like the redwoods, these forests are in danger. In less than a decade, these otherworldly undersea landscapes, lush with life, have all but disappeared along 200 miles of coast north of San Francisco's Golden Gate Bridge.”

   “The Channel Tunnel is the longest undersea tunnel in the world, with this section being 38km (23.6 miles) long.”