Swallow up completely (6)
I believe the answer is:
engulf
'swallow up completely' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for engulf that I've seen before include "Lowered in rank" , "Swallow up, overwhelm" , "Overwhelm; cover totally" , "Immerse, cover completely" , "Deluge" .)