Sailor got posted, but not there (6)
I believe the answer is:
absent
'not there' is the definition.
(I've seen this before)
'sailor got posted' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'got' is a charade indicator (letters next to each other).
'posted' becomes 'sent' ('send' can be a synonym of 'post').
'ab'+'sent'='ABSENT'
'but' acts as a link.
(Other definitions for absent that I've seen before include "Not present or focused" , "elsewhere" , "Forgetful, with mind on other things" , "Missing or dreamy" , "Not present - vacuous" .)