The Hathi Trust Digital Library has placed several historic Irish-English Dictionaries online, at the links indicated below. They are of varying quality, but some might be useful in researching older usages:

O’Brien – 1767 (reprinted 1832): http://catalog.hathitrust.org/Record/009720625
Vallancey – 1802: http://catalog.hathitrust.org/Record/008590418
?, published in Dublin – 1814: http://catalog.hathitrust.org/Record/008684670
O’Reilly – 1830: http://catalog.hathitrust.org/Record/100740586
Coneys – 1849: http://catalog.hathitrust.org/Record/011631745

_________________
I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.