Nouns

(n)firmness, soundnessthe muscle tone of healthy tissue“his muscular firmness”
(n)resoluteness, firmness, firmness of purpose, resolve, resolutionthe trait of being resolute“his resoluteness carried him through the battle”, “it was his unshakeable resolution to finish the work”
(n)firmnessthe property of being unyielding to the touch
(n)steadiness, firmnessthe quality of being steady or securely and immovably fixed in place