Lie about captain's original rank (7)
I believe the answer is:
recline
'lie' is the definition.
(I know that recline is a more specific form of lie)
'captain's original rank' is the wordplay.
'captain's original' becomes 'rec' (I can't explain this - if you can you should believe this answer much more).
'rank' becomes 'line'.
'rec'+'line'='RECLINE'
'about' acts as a link.
Can you help me to learn more?
(Other definitions for recline that I've seen before include "Lie back and relax" , "Lean back to rest" , "Lie back to rest" , "Lie back and take it easy" , "Be recumbent" .)