harmonica vs mouth organ

harmonica and mouth organ both are nouns.

Word	Noun	Adjective	Verb	Adverb
harmonica	Yes	No	No	No
mouth organ	Yes	No	No	No

As nouns, harmonica and mouth organ are synonyms defined as:

harmonica and mouth organ: a small rectangular free-reed instrument having a row of free reeds set back in air holes and played by blowing into the desired hole

Other synonyms of harmonica include harp, mouth harp.

harmonica (noun)	mouth organ (noun)
a small rectangular free-reed instrument having a row of free reeds set back in air holes and played by blowing into the desired hole	a small rectangular free-reed instrument having a row of free reeds set back in air holes and played by blowing into the desired hole