Swallow up; overwhelm (6)
I believe the answer is:
engulf
This clue is a double definition.
'swallow up' is the first definition.
(I've seen this before)
'overwhelm' is the second definition.
(I've seen this before)
(Other definitions for engulf that I've seen before include "'Surround, overwhelm (6)'" , "Swallow up like whirlpool" , "Lowered in rank" , "Deluge" , "Swamp, overwhelm" .)