firmness vs immovableness

firmness and immovableness both are nouns.

Word	Noun	Adjective	Verb	Adverb
firmness	Yes	No	No	No
immovableness	Yes	No	No	No

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

firmness: the quality of being steady or securely and immovably fixed in place
immovableness: not capable of being moved or rearranged

Other hypernyms of firmness include immovability.

firmness (noun)	immovableness (noun)
the quality of being steady or securely and immovably fixed in place	not capable of being moved or rearranged
the trait of being resolute
the property of being unyielding to the touch
the muscle tone of healthy tissue