Allows it to be engulfed by the waves (7)
I believe the answer is:
permits
'allows' is the definition.
('permit' can be a synonym of 'allow')
'it to be engulfed by the waves' is the wordplay.
'to be engulfed by' indicates putting letters inside.
'the waves' becomes 'perms' (perm is a kind of wave).
'it' going into 'perms' is 'PERMITS'.
(Other definitions for permits that I've seen before include "Consents to" , "Allows" .)