The main type of eagle (4)
I believe the answer is:
erne
'type of eagle' is the definition.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for erne that I've seen before include "one that catches fish?" , "Fish-eating sea eagle" , "Marine flyer" , "Sea-eagle in an Irish lake" , "'Sea-eagle, river and lough (4)'" .)