piano accordion vs accordion

piano accordion and accordion both are nouns.

Word	Noun	Adjective	Verb	Adverb
piano accordion	Yes	No	No	No
accordion	Yes	No	No	No

As nouns, accordion is a hypernym of piano accordion; that is, accordion is a word with a broader meaning than piano accordion:

piano accordion: an accordion with a right-hand keyboard
accordion: a portable box-shaped free-reed instrument; the reeds are made to vibrate by air from the bellows controlled by the player

Other hypernyms of piano accordion include squeeze box.

piano accordion (noun)	accordion (noun)
an accordion with a right-hand keyboard	a portable box-shaped free-reed instrument; the reeds are made to vibrate by air from the bellows controlled by the player