Rating or officer – destiny will reveal (7)
I believe the answer is:
matelot
'rating' is the definition.
(I've seen this before)
'officer destiny will reveal' is the wordplay.
I cannot quite see how this works, but
'officer' could be 'mate' (mate is a kind of officer) and 'mate' is present in the answer.
'destiny' could be 'lot' (I've seen this before) and 'lot' is located in the answer.
No letters remain.
This explanation may well be incorrect...
'or' acts as a link.
Can you help me to learn more?
(Other definitions for matelot that I've seen before include "Rating" , "A lot met (anag) - sailor" , "One sailor" , "seafarer" , "One at sea" .)