nickel vs coin

nickel and coin both are nouns.

Word	Noun	Adjective	Verb	Adverb
nickel	Yes	No	Yes	No
coin	Yes	No	Yes	No

As nouns, coin is a hypernym of nickel; that is, coin is a word with a broader meaning than nickel:

nickel (noun)	coin (noun)
a United States coin worth one twentieth of a dollar	a flat metal piece (usually a disc) used as money
five dollars worth of a drug
a hard malleable ductile silvery metallic element that is resistant to corrosion; used in alloys; occurs in pentlandite and smaltite and garnierite and millerite

nickel (verb)	coin (verb)
plate with nickel	form by stamping, punching, or printing
	make up