Take advantage of a sailor needing employment (5)
I believe the answer is:
abuse
'take advantage of' is the definition.
(thesaurus)
'a sailor needing employment' is the wordplay.
'a sailor' becomes 'ab' (abbreviation for able seaman).
'needing' means one lot of letters go next to another.
'employment' becomes 'use' (how something is used).
'ab'+'use'='ABUSE'
(Other definitions for abuse that I've seen before include "Mistreat" , "Violate" , "Treat with cruelty" , "vilification" , "Subject to verbal assault and insults" .)