Sailor trapped in offensive likely to survive (6)
I believe the answer is:
viable
'likely to survive' is the definition.
'sailor trapped in offensive' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'trapped in' means one lot of letters goes inside another.
'offensive' becomes 'vile' (similar in meaning).
'ab' put within 'vile' is 'VIABLE'.
(Other definitions for viable that I've seen before include "Able to survive; practicable" , "Sound" , "Capable of independent life" , "Workable" , "having potential to succeed" .)