fixed costs vs fee

fixed costs and fee both are nouns.

Word	Noun	Adjective	Verb	Adverb
fixed costs	Yes	No	No	No
fee	Yes	No	Yes	No

As nouns, fee is a hyponym of fixed costs; that is, fee is a word with a more specific, narrower meaning than fixed costs:

fixed costs: a periodic charge that does not vary with business volume (as insurance or rent or mortgage payments etc.)
fee: a fixed charge for a privilege or for professional services

Other hyponyms of fixed costs include cover, cover charge, interest, due.

fixed costs (noun)	fee (noun)
a periodic charge that does not vary with business volume (as insurance or rent or mortgage payments etc.)	a fixed charge for a privilege or for professional services
	an interest in land capable of being inherited

fixed costs (verb)	fee (verb)
	give a tip or gratuity to in return for a service, beyond the compensation agreed on