From Longman Dictionary of Contemporary Englishharmonicahar‧mon‧i‧ca /hɑːˈmɒnɪkə $ hɑːrˈmɑː-/ noun [countable] 
APMa small musical instrument that you play by blowing or sucking and moving it from side to side near your mouth SYN mouth organ
APMa small musical instrument that you play by blowing or sucking and moving it from side to side near your mouth SYN mouth organExamples from the Corpus
harmonica• One starts playing a harmonica, the others form a circle.• That is a bluesy harmonica on the title track.• Power, a New Zealander, plays the blues harp and the chromatic harmonica.• She thought about playing her harmonica, but that seemed to be the one thing that wasn't in her bag.• He wheedles his harmonica - a horrible sound.• They ganged up on me and nicked my harmonica.• But he learned to play the harmonica wonderfully.• Brown learned to play guitar, violin, harmonica, piano, mandolin, viola and drums.Origin harmonica (1700-1800) Italian armonica, from Latin harmonia; → HARMONY 