altcoin vs cryptocurrency

altcoin and cryptocurrency both are nouns.

Word	Noun	Adjective	Verb	Adverb
altcoin	Yes	No	No	No
cryptocurrency	Yes	No	No	No

As nouns, cryptocurrency is a hypernym of altcoin; that is, cryptocurrency is a word with a broader meaning than altcoin:

altcoin: an alternative cryptocurrency
cryptocurrency: a currency based on the usage of cryptography to secure transactions

altcoin (noun)	cryptocurrency (noun)
an alternative cryptocurrency	a currency based on the usage of cryptography to secure transactions