One flying flag initially defies all warnings (7)

I believe the answer is:

jackdaw

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

'flag initially defies all warnings' is the wordplay.
'flag' becomes 'jack' (jack is a kind of flag).
'initially' indicates taking the first letters.
The first letters of 'defies all warnings' is 'daw'.
'jack'+'daw'='JACKDAW'

Can you help me to learn more?

(Other definitions for jackdaw that I've seen before include "Thief in Rheims" , "Small species of crow" , "Larcenous member of crow family" , "Grey-headed crow" , "Small member of the crow family" .)

I've seen this clue in The Times.

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