casualness vs variability

casualness and variability both are nouns.

Word	Noun	Adjective	Verb	Adverb
casualness	Yes	No	No	No
variability	Yes	No	No	No

As nouns, variability is a hypernym of casualness; that is, variability is a word with a broader meaning than casualness:

casualness: The state of coming without regularity; of being occasional or incidental.
variability: the quality of being subject to variation

Other hypernyms of casualness include variableness, variance.

casualness (noun)	variability (noun)
a casual manner	the quality of being subject to variation
The state of coming without regularity; of being occasional or incidental.	the quality of being uneven and lacking uniformity