Potential killer when provoked at first (3)

I believe the answer is:

asp

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'potential killer' is the definition.
'asp' can be an answer for 'killer' (Kind of poisonous snake). I am unsure of the 'potential' bit.

'when provoked at first' is the wordplay.
'when' becomes 'as'.
'at first' indicates taking the first letters.
The initial letter of 'provoked' is 'p'.
'as'+'p'='ASP'

Can you help me to learn more?

(Other definitions for asp that I've seen before include "One secreting poison" , "Serpent" , "Snake seen in a spa, strangely" , "Kind of snake - what a sap" , "Pa's Cleopatra's killer" .)

I've seen this clue in The Independent.

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