Green’s Dictionary of Slang

1. (orig. US) a harmonica, a mouth organ.

1887		Scribner’s Mag. Oct. 481/1: She displayed a flimsy red silk handkerchief and a child’s harp .
1903		Ade ‘Why “Gondola” Was Put Away’ in In Babel 40: I’d walked from Loueyville over to Terry Hut with a nigger that played the mouth-harp.
1955		W. Broonzy Big Bill’s Blues 94: Sonny Boy Williamson had a special way of playing the blues on a French harp, better known as a harmonica.
1966		C. Keil Urban Blues 145: [J.B. Lenoir] regards his own talents and those of other prominent bluesmen as God-given gifts, as when describing Jr. Parker as ‘blessed to blow harp’ (harmonica).
1970		K. Mackey Cure 123: He came up there to hear me play. Sat in with me, he’s a gas harp player.
1972		L. Bangs in Psychotic Reactions (1988) 104: I dropped the harp, which was such a limited palette for an experimental artist anyway.
1989		J. Morton Lowspeak.
1997		D.H. Edwards The World Don’t Owe Me Nothing 96: [Howlin’ Wolf] took up the harmonica and made a headway with it. He made his way through with the harp and that voice.
2002		R. Gordon Can’t Be Satisfied 279: [H]e and Mojo Buford have been touring together, dueling with their harps.
2010		K. Richards Life 88: Cyril Davies was a hell of a harp player, one of the best.

2. (US) a vibraharp or vibraphone.

1938

Pic (N.Y.) Mar. 7: jibing the vibes or hitting the harps. — playing the vibraphone.