Disillusion sailor surrounded by neglect (8)
I believe the answer is:
disabuse
'disillusion' is the definition.
(thesaurus)
'sailor surrounded by neglect' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'surrounded by' indicates putting letters inside.
'neglect' becomes 'disuse' (I've seen this before).
'ab' put inside 'disuse' is 'DISABUSE'.
(Other definitions for disabuse that I've seen before include "Undeceive, set right" , "Give correction to" , "Free somebody from an erroneous belief" , "Rid someone (of a mistaken idea)" , "put right" .)