The Ancient Mariner, say, returns for Arabian big fish (4)
I believe the answer is:
emir
'fish' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for emir that I've seen before include "Local chief" , "Islamic chieftain" , "leader in the East" , "Arab leader" , "Eastern ruler in mire" .)