Like his eagle, first Roman emperor is this after October (5)
I believe the answer is:
avian
'like' is the definition.
Although both the answer and definition are adjectives, I don't see how one could define the other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for avian that I've seen before include "Relating to birds" , "Like rails, for example" , "Like a booby" , "Resembling a bird" , "To do with birds - like a dangerous flu" .)