Green’s Dictionary of Slang

(Irish) the buttocks, the behind.

1663		Head Hic et Ubique I vi: Then wid my pishfork I clap him upon de Narsum.
1731		‘Madam Catherine Cadiere’s Case opened’ in ‘Hurlothrumbo’ Bog-house Misc. 7: And then he kiss’d her Narsey-Parsey.