A kingdom termed avian (3)

I believe the answer is:

auk

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

'termed avian' is the definition.
I can't tell whether this definition defines the answer.

'a kingdom' is the wordplay.
'kingdom' becomes 'uk' (UK is an example).
'a'+'uk'='AUK'

Can you help me to learn more?

(Other definitions for auk that I've seen before include "Great ---, extinct seabird" , "A seabird from Milwaukee" , "Northern sea bird with short narrow wings" , "Black/white northern diver" , "Stocky diving bird" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.