self-control vs firmness

self-control and firmness both are nouns.

Word	Noun	Adjective	Verb	Adverb
self-control	Yes	No	No	No
firmness	Yes	No	No	No

As nouns, firmness is a hypernym of self-control; that is, firmness is a word with a broader meaning than self-control:

Other hypernyms of self-control include firmness of purpose, resoluteness, resolution, resolve.

self-control (noun)	firmness (noun)
the act of denying yourself; controlling your impulses	the quality of being steady or securely and immovably fixed in place
the trait of resolutely controlling your own behavior	the trait of being resolute
	the property of being unyielding to the touch
	the muscle tone of healthy tissue