"life forms of the deep ocean and sea floor," 1891, coined by Haeckel from Greek benthos "depth of the sea," related to bathos "depth," bathys "deep," of unknown origin. Adjective benthic is attested from 1902.
The organisms living on sea or lake bottoms. The benthos are divided into sessile organisms (those that are attached to the bottom or to objects on or near the bottom) and vagrant organisms (those that crawl or swim along the bottom). Compare nekton, plankton. See more at epifauna, infauna.