Whole triangle is out of kilter (8)

I believe the answer is:

integral

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

'triangle is out of kilter' is the wordplay.
'triangle' anagrams to 'INTEGRAL'.
Though, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for integral that I've seen before include "Inbuilt, essential" , "Triangle being essential" , "A component and indispensable part of, like triangle" , "contributing to unity" , "Relating to being complete" .)

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

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