fluctuation vs unregularity

fluctuation and unregularity both are nouns.

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

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

fluctuation: the quality of being unsteady and subject to changes
unregularity: not characterized by a fixed principle or rate; at irregular intervals

Other hypernyms of fluctuation include irregularity.

fluctuation (noun)	unregularity (noun)
the quality of being unsteady and subject to changes	not characterized by a fixed principle or rate; at irregular intervals
an instance of change; the rate or magnitude of change
a wave motion