Green’s Dictionary of Slang

1. an Irishman.

1821		‘A Real Paddy’ Real Life in Ireland 186: When the hour of nine hath striken, / Up the nine stairs slow we crawl; / Crowds of Pads the alleys thicken, / That convey them to straw hall.
1987		(con. 1920s) L. Redmond Emerald Square 13: Thought you were strictly for the Pads?

2. a nickname or intimate form of address for an Irishman.

1855		‘Irish Love letters’ in Diprose’s Comic Song Book 3: Here’s a letter just sent her by Pad.
1958		(con. 1940s) B. Behan Borstal Boy 95: Nay, you silly feller [...] ’tis all one day, Pad.