Ó Dálaigh, Máirín (née Nic Dhiarmada ) (c.1909–94), Celticist and lexicographer, was born in Mussoorie, United Provinces of India and Kashmir. Both her parents were Irish and living in India as her father was a teacher with the Munster fusiliers. At the age of two and a half she was sent home to Ireland to receive an education. She never got to know her father properly although her mother returned to Ireland occasionally. According to one account, she was diagnosed with tuberculosis as a young child and sent to Menton in the south of France to recuperate. Her father visited her there but she failed to recognise him at the railway station although she had a photograph of him. On arriving in Ireland she first lived with her paternal aunt in Tralee, Co. Kerry, but did not have a good relationship with her. She received her earliest education in the Dominican School, Cabra, Dublin. Subsequently she attended Scoil an Chreidimh Ró-Naofa in Skerries and afterwards the Loreto convent, Balbriggan, and the Dominican sisters in Eccles Street, Dublin. She matriculated to UCD where she studied for an honours degree in Latin and Irish, graduating BA in 1932, and subsequently obtaining an H.Dip. Ed. While a student she became a committee member of the Literary and Historical Society as well as a committee member of An Chumann Gaelach (1930–31). She was elected reachtaire of the latter society in 1931. During her time as a member of these societies she became friends with her future husband, Cearbhall Ó Dálaigh (qv), who was also active in both. The couple married on 14 June 1934 and spent their honeymoon visiting the Gaeltacht islands; they did not have any children.
After leaving university she taught in Monaghan and afterwards in Scoil Chaitríona, Glasnevin, Dublin. A year after her marriage, she decided to return to academia. She followed the advice of Osborn Bergin (qv) to prepare for a year before undertaking an MA in old Irish, graduating in 1939. Her thesis was based on the verbal system of An leabhair Laighnigh (Lebar na Nuachongbála) of Táin Bó Cuailgne. Bergin was impressed by her abilities and she was appointed assistant in the Old Irish department in UCD. She was highly regarded as a scholar and devoted most of her life to working on the RIA's Dictionary of the Irish language, based primarily on Old and Middle Irish sources. From the 1940s onwards, she published articles on philology, the history of Old Irish, numerous reviews of academic works as well as editions of texts in journals such as Éigse, Ériú, Celtica, Irish Historical Studies, Béaloideas and An Sagart. Her reviews included those on The Irish tradition by Robin Flower (qv), James Carney's (qv) Poems of the Butlers and Máire Mhac an tSaoi's Dhá sgéal artúraíochta. She compiled a substantial glossary contained in Beatha Aodha Ruaidh Uí Dhomhnaill 2 (1957), edited by Pól Breathnach and Colm Ó Lochlainn (qv). She published an edition of Cath Maige Mucrama in 1975 for the Irish Texts Society. It was a great disappointment to her that this book was never reviewed as she had spent a number of years working on it. She also contributed to Myles Dillon's (qv) Irish sagas (1950), James Carney's Early Irish poetry (1965) and James Carney and David Greene (qv) (eds.), Celtic studies: essays in memory of Angus Matheson 1912–1962 (1968).
Elected MRIA on 16 March 1954, she acted as external examiner of old Irish for the NUI during the 1960s, and served as a government nominee on the UCD governing body from 1958 to 1970 and again from 1979 to 1982; she was too a member of the board of the School of Celtic Studies at the DIAS.
Although she loved to travel, she went out of her way to avoid travelling either to or through England. The couple moved to Luxembourg in 1973 on her husband's appointment as the Irish member of the EEC's Court of Justice. The following year, on Cearbhall Ó Dálaigh's inauguration as president of Ireland, the couple moved to Áras an Uachtaráin. Commenting later on the two years she spent in the Áras, she stated that they were ‘boring’ as she had been cut off from friends and family (Sunday Independent, 2 Oct. 1983).
Ó Dálaigh received a number of degrees and awards. Together with her husband, she was awarded an honorary D.Litt.Celt. by the NUI in 1975. The Italian government awarded her the commendatore (al remito). She officially opened Oireachtas na Gaeilge 1979 which was held in Dublin city.
On her husband's resignation as president (1976), the couple moved to Kerry and bought a house near Sneem. After his death (1978) she presented UCD with a number of paintings and art works, including Louis Le Brocquy's Táin series.
Towards the end of her life Ó Dálaigh suffered from a debilitating illness. She died 25 January 1994 and was buried beside her husband in Sneem, Co. Kerry. She bequeathed a third of her assets to Pádraig Ó Fiannachta who used the bequest to purchase the library she had collected with her husband, consisting of 2,000 volumes, some rare. The library was donated to Ionad an Bhlascaoid in Dún Chaoin. In addition, Fr Ó Fiannachta used a portion of the bequest to commission a mural for a wall in her memory in Seipéal Chaitlíona, Ventry, Co. Kerry.