Wiktionary
moral fibre
alt. (context UK English) The inner strength to do what one believes to be right; often an ability to make difficult decisions. n. (context UK English) The inner strength to do what one believes to be right; often an ability to make difficult decisions.
Usage examples of "moral fibre".
Or perhaps he felt that the Captain needed a little stiffening of the moral fibre.
With his democratical notions, that wicked fellow Jefferson has rotted the moral fibre of the whole country.