variability vs unregularity

variability and unregularity both are nouns.

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

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

variability: the quality of being uneven and lacking uniformity
unregularity: not characterized by a fixed principle or rate; at irregular intervals

Other hypernyms of variability include irregularity.

variability (noun)	unregularity (noun)
the quality of being subject to variation	not characterized by a fixed principle or rate; at irregular intervals
the quality of being uneven and lacking uniformity