imperturbability vs calmness

imperturbability and calmness both are nouns.

Word	Noun	Adjective	Verb	Adverb
imperturbability	Yes	No	No	No
calmness	Yes	No	No	No

As nouns, calmness is a hypernym of imperturbability; that is, calmness is a word with a broader meaning than imperturbability:

imperturbability (noun)	calmness (noun)
calm and unruffled self-assurance	steadiness of mind under stress
	a feeling of calm; an absence of agitation or excitement
	an absence of strong winds or rain