Crossword Genius

Like his eagle, first Roman emperor is this after October (5)

Ross

I believe the answer is:

avian

I'm a little stuck... Click here to teach me more about this clue!

'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" .)

I've seen this clue in The Times.
Want a hint initially instead of a full solution? Install my app