departure vs fluctuation

departure and fluctuation both are nouns.

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

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

Other hypernyms of departure include variation.

departure (noun)	fluctuation (noun)
the act of departing	the quality of being unsteady and subject to changes
euphemistic expressions for death	an instance of change; the rate or magnitude of change
a variation that deviates from the standard or norm	a wave motion