1. Of or pertaining to ocean-depths exceeding 1,000 fathoms or happening on the bottom under a body of water: In the book Timothy was reading, he learned that a benthon was an accumulation of organisms that live in the benthal region of the sea.
2. Relating to the deepest zone or region of the ocean: Jane really wondered how anything could survive in the benthal expanse of any sea, being so dark and without light.