Unexpectedly greet flyer (5)

I believe the answer is:

egret

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'flyer' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'unexpectedly greet' is the wordplay.
'unexpectedly' indicates an anagram.
'greet' with letters rearranged gives 'EGRET'.

Can you help me to learn more?

(Other definitions for egret that I've seen before include "Seabird" , "One of a pair of waders" , "Lesser white heron" , "Heron-like wader" , "Type of heron" .)

I've seen this clue in The Mirror.

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