Sailor, not manned, organised desertion (11)
I believe the answer is:
abandonment
'desertion' is the definition.
(synonyms)
'sailor not manned organised' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'organised' is an anagram indicator.
'not'+'manned'='notmanned'
'notmanned' is an anagram of 'andonment'.
'ab'+'andonment'='ABANDONMENT'
(Other definitions for abandonment that I've seen before include "leaving" , "Act of desertion" , "surrender" , "being neglected" , "Process of giving up completely" .)