partsong vs song

partsong and song both are nouns.

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

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

Other hypernyms of partsong include vocal.

partsong (noun)	song (noun)
a song with two or more voice parts	the act of singing
	a short musical composition with words
	the characteristic sound produced by a bird
	a distinctive or characteristic sound
	a very small sum