O'Rahilly (Ní Rathaille, Ó Rathaille), Cecile (Sisile) (1894–1980), Celticist and literary scholar, was born 17 December 1894 in Listowel, Co. Kerry, eleventh among thirteen surviving children of Thomas Francis Rahilly, court clerk, and Julia Mary Rahilly (née Curry) from Glin, Co. Limerick. She was directly descended from a brother of the poet Aodhagán Ó Rathaille (qv) on her father's side and her mother was a grandniece of the scholar Eugene O'Curry (qv). Michael Joseph O'Rahilly (qv), a prominent nationalist who was killed in the 1916 rising, was her uncle. Two of her siblings, Thomas Francis O'Rahilly (qv) and Alfred O'Rahilly (qv), also had prestigious academic careers. Cecile received her earliest education in the local national school in Listowel. Seven years after her father's death (1899), the family moved to Dublin and she continued her education in the Dominican College, Eccles St. She matriculated to UCD in 1912, graduating with a first-class honours degree in Celtic studies in 1916. Osborn Bergin (qv) wrote a praise poem in her honour to mark the occasion.
The same year, she won a travelling scholarship and moved to Bangor, north Wales, to study under John Morris-Jones and Ifor Williams. The latter considered her to be the best pupil he ever had. During her time in Bangor, what was to become a lifelong friendship developed between herself and fellow student Myfanwy Williams. She was awarded an MA degree in 1919. On graduating she began teaching French in Beaumaris Grammar School, Anglesey, and remained there until 1928, when she moved to Cardiff to take up a post in Cardiff High School for Girls. She was proficient in Welsh and won an award at the 1920 National Eisteddfod of Wales with an essay on Ireland's relationship with Wales between AD 1055 and 1200. This was later expanded and published under the title Ireland and Wales: their historical and literary relations (1924). Another work, The pursuit of Gruaidh Grian-sholas was published the same year for the Irish Texts Society. She does not appear to have published any further academic works until 1949.
In 1946 she returned to Ireland to take up an assistant professorship in the School of Celtic Studies at the Dublin Institute for Advanced Studies. She was later appointed professor in 1956, the first woman ever to hold such a post in the school. Her brother Thomas was director of the school at the time, and under his direction she edited Five seventeenth-century political poems (1946), Eachtra Uilliam (1949), and Trompa na bhFlaitheas (1955). She appears to have stood in the shadow of her older brother while he lived. After his death (1953), the focus of her research shifted to Táin Bó Cuailgne. She edited the three main recensions of the work. The Stowe version of Táin Bó Cuailgne was published in 1961 and was followed by Cath Finntrágha (1962), Táin Bó Cuailgne from the Book of Leinster (1967), and Táin Bó Cuailgne: recension 1 (1976). D. A. Binchy (qv) notes that not only did she provide reliable translations and texts, she also included an elaborate apparatus of grammatical notes (Ir. Times, 14 May 1980). She had almost completed an analytical study of the Táin before she died; it is unclear whether her intention had been to publish this as a monograph or as a substantial article. She also contributed to a number of academic journals including Éigse, Ériu, Celtica, Studia Celtica, Revue celtique, Bulletin of the Board of Celtic Studies, Bibliotheca Celtica, Bibliographie linguistique, Indogermanisches Jahrbuch, Zeitschrift für celtische Philologie and The Year's Work in Modern Language Studies. During her time in the School of Celtic Studies she also contributed to the ‘Dictionary of Classical Irish’ project initiated by her brother Thomas. This dictionary was never published.
After her retirement in December 1964 she was appointed external research worker by the School of Celtic Studies. Continuing her academic work, she published two further books and more than twenty articles. She was awarded a D.Litt.Celt. degree by the NUI (19 January 1957), elected MRIA (16 March 1966), and awarded a D.Litt. honoris causa by the NUI (31 January 1977).
She had always suffered from a delicate constitution, and particularly towards the end of her life her health and sight began to fail. Her friend Myfanwy Williams had moved to Dublin to live with her in May 1951, taking care of her until her death. O'Rahilly, who never married, died 2 May 1980 and is buried in Glasnevin cemetery, Dublin.