Doctor in casualty first to recognise warning sign (5)

I believe the answer is:

amber

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'warning sign' is the definition.
'amber' can be an answer for 'warning' (amber traffic light). I'm not certain of the 'sign' bit.

'doctor in casualty first to recognise' is the wordplay.
'doctor' becomes 'mb' (Bachelor of Medicine).
'in' means one lot of letters goes inside another.
'casualty' becomes 'ae' (abbreviation for Accident and Emergency).
'first to' indicates taking the first letters.
The initial letter of 'recognise' is 'r'.
'mb' going into 'ae' is 'ambe'.
'ambe'+'r'='AMBER'

Can you help me to learn more?

(Other definitions for amber that I've seen before include "Yellow fossil-resin" , "Name of female" , "Cautionary colour" , "Prepare-to-stop signal" , "Follilised resin" .)

I've seen this clue in The Times.

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