fixed cost vs fee

fixed cost and fee both are nouns.

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

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

fixed cost: 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 cost include cover, cover charge, interest, due.

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