Submerge (5)
I believe the answer is:
drown
'submerge' is the definition.
(I know that submerge can be written as drown)
This is all the clue.
(Other definitions for drown that I've seen before include "Die in water" , "Submerge, maybe fatally" , "Sink" , "Swamp" , "Completely conceal" .)