Severe internal gastric troubles (6)

I believe the answer is:

strict

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

'severe' is the definition.
(I've seen this before)

'internal gastric troubles' is the wordplay.
'STRICT' is hidden within the letters.
But, I'm not sure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for strict that I've seen before include "Requiring exact obedience or compliance with rules" , "Authoritarian" , "Not lenient or indulgent" , "Not allowing laxity" , "Exacting, severe, rigid" .)

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

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