koto vs stringed instrument

koto and stringed instrument both are nouns.

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

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

koto: Japanese stringed instrument that resembles a zither; has a rectangular wooden sounding board and usually 13 silk strings that are plucked with the fingers
stringed instrument: a musical instrument in which taut strings provide the source of sound

koto (noun)	stringed instrument (noun)
Japanese stringed instrument that resembles a zither; has a rectangular wooden sounding board and usually 13 silk strings that are plucked with the fingers	a musical instrument in which taut strings provide the source of sound