retainer vs fee

retainer and fee both are nouns.

Word	Noun	Adjective	Verb	Adverb
retainer	Yes	No	No	No
fee	Yes	No	Yes	No

As nouns, fee is a hypernym of retainer; that is, fee is a word with a broader meaning than retainer:

retainer (noun)	fee (noun)
a dental appliance that holds teeth (or a prosthesis) in position after orthodontic treatment	a fixed charge for a privilege or for professional services
a person working in the service of another (especially in the household)	an interest in land capable of being inherited
a fee charged in advance to retain the services of someone

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