Crossword Genius

Temper of Jack, leaving hurt (5)

Ross

I believe the answer is:

inure

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

I cannot understand how the remainder of the clue works.

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(Other definitions for inure that I've seen before include "Harden, habituate" , "Steel" , "Cause to become hardened to" , "Accustom (someone) to something unpleasant" , "Get used to conditions" .)

I've seen this clue in The Telegraph.
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