Bottom of the ocean (6)
I believe the answer is:
seabed
'bottom of the ocean' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for seabed that I've seen before include "Davy Jones's locker" , "marine base" , "The ocean floor, not for sleeping" , "Bottom of the ocean" , "Debase (anag)" .)