Cannot check without incision (5)

I believe the answer is:

notch

I'm a little stuck... Click here to teach me more about this clue!

'incision' is the definition.
(synonyms)

'cannot check without' is the wordplay.
'NOTCH' is hidden in amongst the letters.
But, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for notch that I've seen before include "Cleft" , "V-shaped nick" , "Secure" , "Small V-shaped cut or indentation" , "Indentation, nick" .)

I've seen this clue in the Sydney Morning Herald.

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