Saboteur losing heart becomes more virtuous (6)

I believe the answer is:

nobler

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'more virtuous' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for nobler that I've seen before include "More honourable" , "More aristocratic" , "More illustrious" , "'Whether 'tis ... in the mind, to suffer the slings and arrows of outrageous fortune''/Hamlet" , "''Whether 'tis ... in the mind to suffer / The slings and arrows of outrageous fortune'' (Hamlet)" .)

I've seen this clue in The Times.

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