Invective for a sailor to employ (5)
I believe the answer is:
abuse
'invective' is the definition.
(thesaurus)
'a sailor to employ' is the wordplay.
'a sailor' becomes 'ab' (abbreviation for able seaman).
'to employ' becomes 'use' (synonyms).
'ab'+'use'='ABUSE'
'for' acts as a link.
(Other definitions for abuse that I've seen before include "Insulting language" , "Treat badly; insult" , "Misemploy - invective" , "Ill-treatment" , "Inveigh against" .)