Citations:tilly

an extra given to a customer at no additional charge, a lagniappe

 * 1909, The Fortnightly Review, volume 91, page 782:
 * A “tilly” (Gael. Thuille=more) is the extra drop of milk poured over measure by your milkman.


 * (not CFI-independent of the other Joyce citation, and too mentiony to count anyway, but still usefully clarificatory)


 * 2000, John P. Anderson, Finding Joy in Joyce: A Readers Guide to Ulysses, page 72:
 * the rural word "tilly," an extra measure not paid for,

something extra, an added bonus?

 * 1798, J. Frazer, Edward Molloy (ballad), in The Ballads of Ireland Collected and Edited by Edward Hayes, volume 1 (1855):
 * Ay, call me a traitor, though traitorous rogue Is below me as much as the nails in my brogue; But ye shall not be led, our good cause to destroy, And ourselves for a tilly, by Edward Molloy.

???

 * 1875, The Dublin University Magazine, volume 85:
 * "I had me eye out in case he had done ye a bad turn; may be he did, an' may be he didn't, but I put a tilly in this just to sarve him out," and he drew a heavy pistol from his pocket as he spoke.