Inattentive sailor dismissed (6)
I believe the answer is:
absent
'inattentive' is the definition.
('absent' can be similar in meaning to 'inattentive')
'sailor dismissed' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'dismissed' becomes 'sent' (I've seen this in other clues).
'ab'+'sent'='ABSENT'
(Other definitions for absent that I've seen before include "elsewhere" , "Missing or dreamy" , "Away" , "Not attending" , "nowhere to be seen" .)