piano quartet vs quartette

piano quartet and quartette both are nouns.

Word	Noun	Adjective	Verb	Adverb
piano quartet	Yes	No	No	No
quartette	Yes	No	No	No

As nouns, quartette is a hypernym of piano quartet; that is, quartette is a word with a broader meaning than piano quartet:

piano quartet: a group of four players, including a piano player, a violin player, a viola player and a cello player.
quartette: four performers or singers who perform together

Other hypernyms of piano quartet include quartet.

piano quartet (noun)	quartette (noun)
a group of four players, including a piano player, a violin player, a viola player and a cello player.	a musical composition for four performers
	four people considered as a unit
	a set of four similar things considered as a unit
	four performers or singers who perform together