Frustrate with war-torn stretch (6)

I believe the answer is:

thwart

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

'frustrate' is the definition.
(I know that frustrate can be written as thwart)

'with war-torn stretch' is the wordplay.
'THWART' is hidden within the letters.
However, I am uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for thwart that I've seen before include "Oppose successfully" , "Snooker" , "Stymie" , "Hinder or prevent" , "Frustrate, prevent from doing" .)

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

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