banjo vs stringed instrument

banjo and stringed instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
banjo	Yes	No	No	No
stringed instrument	Yes	No	No	No

As nouns, stringed instrument is a hypernym of banjo; that is, stringed instrument is a word with a broader meaning than banjo:

banjo: a stringed instrument of the guitar family that has long neck and circular body
stringed instrument: a musical instrument in which taut strings provide the source of sound

banjo (noun)	stringed instrument (noun)
a stringed instrument of the guitar family that has long neck and circular body	a musical instrument in which taut strings provide the source of sound