The Collaborative International Dictionary of English v.0.48:

Benthos \Ben"thos\ (b[e^]n"th[o^]s), n. [NL., fr. Gr. be`nqos
   depth of the sea.]
   The bottom of the sea, esp. of the deep oceans; hence (Bot. &
   Zool.), the fauna and flora of the sea bottom; -- opposed to
   plankton.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

benthos
    n 1: a region including the bottom of the sea and the littoral
         zones [syn: benthos, benthic division, benthonic
         zone]
    2: organisms (plants and animals) that live at or near the
       bottom of a sea

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "benthos":
   Bassalia, Loch Ness monster, abyss, abyssal zone, alevin,
   bathyal zone, benthon, bottom waters, bottomless depths, cetacean,
   dolphin, fingerling, fish, fry, game fish, grilse, ground,
   inner space, kipper, man-eater, man-eating shark, marine animal,
   minnow, minny, nekton, ocean bottom, ocean depths, ocean floor,
   panfish, pelagic zone, plankton, porpoise, salmon, sea monster,
   sea pig, sea serpent, sea snake, shark, smolt, sponge, the deep,
   the deep sea, the deeps, the depths, trench, tropical fish,
   whale