song vs buy

song and buy both are nouns.

Word	Noun	Adjective	Verb	Adverb
song	Yes	No	No	No
buy	Yes	No	Yes	No

As nouns, buy is a hypernym of song; that is, buy is a word with a broader meaning than song:

Other hypernyms of song include bargain, steal.

song (noun)	buy (noun)
the act of singing	an advantageous purchase
a short musical composition with words
the characteristic sound produced by a bird
a distinctive or characteristic sound
a very small sum

song (verb)	buy (verb)
	accept as true
	obtain by purchase; acquire by means of a financial transaction
	make illegal payments to in exchange for favors or influence
	acquire by trade or sacrifice or exchange
	be worth or be capable of buying