Haliday, William (1788–1812), Irish–language scholar and linguist, was born at 32 Arran Quay, Dublin, eldest among three sons of Dr William Haliday, apothecary, originally of Carrick–on–Suir, Co. Tipperary. His father encouraged him to pursue law, and on his qualifying as a solicitor his godfather, John Toler (qv), Lord Norbury, appointed him deputy filacer in his court.
In 1805 he began studying the Irish language with the help of three Munstermen who lived in Dublin, Mac Faelchú, Ó Conaill, and (Mícheál?) Ó Cathasaigh. Having been raised in an atmosphere hostile to Irish culture and perhaps fearing his father's disapproval, he assumed the name ‘William O'Hara’ when he began his lessons. He was one of the founding members of the Gaelic Society of Dublin, which was established in December 1806 with the goal of promoting a better understanding of the literature and antiquities of Gaelic Ireland. The following year he met George Petrie (qv) and began teaching him Irish in return for drawing lessons.
Haliday published Uraicecht na Gaedhilge: a grammar of the Irish language in 1808, under the initials E. O'C., which stood for ‘Edmund O'Connell’, another of his pseudonyms. This work is regarded as superior to other such works published before and after it, and is particularly remarkable considering the fact that it was written while Haliday was still only 19 and had begun learning Irish just a few years earlier. His text and translation of a first volume of the history of Ireland by Geoffrey Keating (qv) was published anonymously in 1811, the first time the original text appeared in print. By the time of his early death he had acquired a considerable knowledge of Latin, Greek, Hebrew, Persian, Sanskrit, and Arabic and was working on a dictionary of modern Irish. The materials for this were passed on to Edward O'Reilly (qv) and used by him in his Irish–English dictionary (published 1817).
In February 1812 Haliday married a Miss Alder, daughter of a Dublin merchant. His health had begun to decline, however, and he died on 26 October 1812. He was buried in Dundrum cemetery, Dublin. A monument to his memory was erected there by his widow. His epitaph was composed by his friend and fellow founding-member of the Gaelic Society, the Rev. John Lanigan (qv).