from Edward Bunting, The Ancient Music of Ireland (Dublin 1840), page 21: The strings of the harp.
Irish comhluí
spoken by Gráinne Yeats
Scottish Gaelic co-laighe
spoken by Tony Dilworth
Click the play button to hear it spoken. help
This short video clip shows how comhluighe acts as a 'placemarker'; as the strings are unmarked, the harper is able to orient themselves by strumming along the harp to find comhluighe.
Simon Chadwick 2008
Caomhluighe - Lying together
Bunting's footnote adds: 'Called by the harpers "The Sisters", were two strings in unison...' The English version suggests that word intended was comhluighe, a compound attested in the early literature to denote 'act of lying, sleeping together'; in modern spelling this would be comhluí. Bunting is here consistent in using caomh-, but on p.32 he writes Comh luighe, 'Equally stretched'.
On the other hand there is an old word coblach which appears to denote some kind of music, and its plural occurs once in the early literature (in the dative, na coblaigib). The plural obviously brings the term closer to the English 'sisters' and it may be, therefore, that comhluí and 'lying together' merely represent fanciful etymologies: Bunting has no instance of na, the plural article, preceding his c(a)omhluighe.
It is unfortunate that not enough is yet known about coblach. Ann Heymann draws my attention to a statement made in 1849 by Patrick Byrne (c.1784-1863), perhaps the last of the harpers (Music and Letters XXIV [1943], p.102): "These two unison notes are sometimes called, and in ancient times were called, Ne Cawlee - or the companions. Afterwards they were called the Sisters." The form Ne (for na) shows that Byrne understood his Cawlee to be plural, possibly cobhlaigh (plural of cobhlach, the modern spelling of coblach); but we seem to have no evidence as to Byrne's competence in the Irish language.
Colm Ó Baoill 2002