Green’s Dictionary of Slang

a member of the Irish nationalist movement Sinn Fein.

1954–56		B. Behan ‘The Same Again, Please’ in After the Wake (1981) 111: It ’ung over the canteen counter – Beware – in black and red wool, till the Shinners let off a landmine.
1987		(con. 1920s) L. Redmond Emerald Square 7: He was a member of the guerilla force that broke the power of the British in the twenty-six counties, a ‘Shinner’.
1997		Irish Times 22 Feb. n.p.: He called Catholics ‘Shinners’ [BS].