A British flier (3)
I believe the answer is:
auk
'flier' is the definition.
(auk is a kind of birdanimal)
'a british' is the wordplay.
'british' becomes 'uk' (I've seen this in other clues).
'a'+'uk'='AUK'
(Other definitions for auk that I've seen before include "Northern sea-bird with short narrow wings" , "Short-winged seabird" , "Diving sea bird" , "Great ---, extinct seabird" , "Northern sea bird with short narrow wings" .)