Mostly respect a large naval officer (7)
I believe the answer is:
admiral
'naval officer' is the definition.
'mostly respect a large' is the wordplay.
'mostly' means to remove the last letter.
'respect' becomes 'admire' (admiring is a kind of respecting).
'a large' becomes 'al' (I can't explain this - if you can you should give a lot more credence to this answer).
'admire' with its final letter removed is 'admir'.
'admir'+'al'='ADMIRAL'
Can you help me to learn more?
(Other definitions for admiral that I've seen before include "Top-ranking naval officer" , "[NELSON] perhaps" , "Blake, for one" , "Eg, Nelson" , "Navy rank" .)