Green’s Dictionary of Slang

harp n.1

[the reverse of an Irish coin once pictured Hibernia and her harp, the ‘national instrument’ of Ireland]

1. [late 18C–mid-19C] a woman.

2. [late 18C+] (Irish) the ‘tail’ (reverse side) of coin; thus a halfpenny minted in Ireland.

3. [late 19C+] (US) an Irish person.

SE in slang uses

In phrases

play the harp (v.) (also play a harp) [the harp-playing angels of heaven]

[late 19C+] to die.