business cycle vs fluctuation

business cycle and fluctuation both are nouns.

Word	Noun	Adjective	Verb	Adverb
business cycle	Yes	No	No	No
fluctuation	Yes	No	No	No

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

business cycle: recurring fluctuations in economic activity consisting of recession and recovery and growth and decline
fluctuation: an instance of change; the rate or magnitude of change

Other hypernyms of business cycle include variation.

business cycle (noun)	fluctuation (noun)
recurring fluctuations in economic activity consisting of recession and recovery and growth and decline	the quality of being unsteady and subject to changes
	an instance of change; the rate or magnitude of change
	a wave motion