double reed vs reed instrument

double reed and reed instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
double reed	Yes	No	No	No
reed instrument	Yes	No	No	No

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

double reed: a woodwind that has a pair of joined reeds that vibrate together
reed instrument: a musical instrument that sounds by means of a vibrating reed

Other hypernyms of double reed include beating-reed instrument, reed.

double reed (noun)	reed instrument (noun)
a pair of joined reeds that vibrate together to produce the sound in some woodwinds	a musical instrument that sounds by means of a vibrating reed
a woodwind that has a pair of joined reeds that vibrate together