A United Kingdom bird (3)

I believe the answer is:

auk

'bird' is the definition.
(auk is a kind of bird)

'a united kingdom' is the wordplay.
'united kingdom' becomes 'UK' (synonyms).
'a'+'uk'='AUK'

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

I've seen this clue in The Globe and Mail.

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