Certain to succeed (4-4)

I believe the answer is:

sure-fire

'certain to succeed' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for sure-fire that I've seen before include "Certain of success" , "Dead cert" , "Infallible" , "Certain to succeed - a positive conflagration?" .)

I've seen this clue in The Guardian.

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