music box vs musical instrument

music box and musical instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
music box	Yes	No	No	No
musical instrument	Yes	No	No	No

As nouns, musical instrument is a hypernym of music box; that is, musical instrument is a word with a broader meaning than music box:

music box: produces music by means of pins on a revolving cylinder that strike the tuned teeth of a comb-like metal plate
musical instrument: any of various devices or contrivances that can be used to produce musical tones or sounds

Other hypernyms of music box include instrument.

music box (noun)	musical instrument (noun)
produces music by means of pins on a revolving cylinder that strike the tuned teeth of a comb-like metal plate	any of various devices or contrivances that can be used to produce musical tones or sounds