string quartette vs string quartet

string quartette and string quartet both are nouns.

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

As nouns, string quartette and string quartet are synonyms defined as:

string quartette and string quartet: an instrumental quartet with 2 violins and a viola and a cello

string quartette (noun)	string quartet (noun)
an instrumental quartet with 2 violins and a viola and a cello	an instrumental quartet with 2 violins and a viola and a cello