fixed charge vs fee

fixed charge and fee both are nouns.

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

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

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

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