Indefinite truce in an engagement (9)

I believe the answer is:

uncertain

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'indefinite' is the definition.
(similar in meaning)

'truce in an engagement' is the wordplay.
'truce in an' can be anagrammed to 'UNCERTAIN'.
However, I'm unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for uncertain that I've seen before include "In doubt" , "Not convinced" , "Changeable" , "Not definite" , "Not at all sure or decided" .)

I've seen this clue in The Globe and Mail and The Guardian.

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