Inundate, overwhelm (6)
I believe the answer is:
engulf
I believe this clue is a double definition.
'inundate' is the first definition.
(I've seen this before)
'overwhelm' is the second definition.
(I've seen this in another clue)
(Other definitions for engulf that I've seen before include "Completely swamp" , "Flu gen (anag) - overwhelm" , "Completely overwhelm" , "'Surround, overwhelm (6)'" , "Overwhelm; cover totally" .)