Tomás Mac Donnchadha de Bhaldraithe, Irish scholar notable for his work on the Irish language, particularly in the field of lexicography, is born on December 14, 1916, in Ballincurra, County Limerick. He is best known for his English-Irish Dictionary, published in 1959.

De Bhaldraithe is born Thomas MacDonagh Waldron, one of five children of Pádraig de Bhaldraithe, civil servant from Nenagh, County Tipperary, and Eilís Nic Conmara from near Kilkee, County Clare. He is named after Thomas MacDonagh, one of the signatories of the Proclamation of the Irish Republic, who had been executed after the Easter Rising earlier that year. He moves to Donnybrook, Dublin, with his family at the age of five. He is enrolled in Muckross Park school in 1923. He receives his secondary education at Belvedere College in Dublin (1926-34). He adopts the use of the Irish language version of his name in both Irish and English.

De Bhaldraithe’s stance on standard forms and spellings is supported by Éamon de Valera despite opposition from traditionalists in the Department of Education, and the work is widely seen as an important benchmark in Irish scholarship.

In 1942, de Bhaldraithe is appointed a professor at the Dublin Institute for Advanced Studies (DIAS) in the department of Celtic Studies. In 1960 he is appointed professor of modern Irish language and literature at University College Dublin (UCD), where he develops an impressive archive of material on Irish dialects. Much of the material in this archive is later used as the basis of Niall Ó Dónaill‘s Foclóir Gaeilge-Béarla, published in 1978, for which he is consulting editor. Also, during the 1970s, de Bhaldraithe translates the Irish language diary of Amhlaoibh Ó Súilleabháin, Cín Lae Amhlaoibh, into English. It is then published by Mercier Press as The Diary of an Irish Countryman.

The language laboratory which de Bhaldraithe sets up in UCD is the first of its kind in any university in Ireland. His interest in seanchas (folklore) leads to his publication of Seanchas Thomáis Laighléis in 1977, while his earlier work includes the ground-breaking study of the Cois Fharraige dialect (a variety of Connacht Irish), Gaeilge Chois Fharraige: Deilbhíocht. In later years he works extensively on the definitive Irish dictionary, Foclóir Stairiúil na Nua-Ghaeilge, which remains unfinished at the time of his death, but which is still in progress today.

De Bhaldraithe dies in Dublin on April 24, 1996, after launching a collection of a friend’s writings entitled The words we use. He marries Vivienne Ní Thoirdhealbhaigh in 1943 and they have nine children.