Ultimately, that which surpasses the limits of endurance (3,3)

I believe the answer is:

the end

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'endurance' is the definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for the end that I've seen before include "special person" , "Final words on screen" , "last line of story" , "Words on last page" .)

I've seen this clue in the Evening Standard.

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