Sailor forced oil into ending (9)
I believe the answer is:
abolition
'ending' is the definition.
(abolition is a kind of ending)
'sailor forced oil into' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'forced' indicates an anagram.
'oil'+'into'='oilinto'
'oilinto' with letters rearranged gives 'olition'.
'ab'+'olition'='ABOLITION'
(Other definitions for abolition that I've seen before include "Action of doing away with something" , "Eradication" , "Removal of" , "Annulment" , "Complete ending (of something)" .)