Formed or situated or occurring beneath the ocean or the ocean bed(adjective)
WordNet. Princeton University. 2010.
Use "subocean" in a sentence
"It may sound grand and noble to forbid all nations from annexing or militarizing the subocean territories."
"Such an explosion, indescribable in its fury, might in the end raise the height of the subocean island a foot."
"And then one day, at the northwest end of the subocean rupture, an eruption of liquid rock occurred that was different from any others that had preceded."