sean nósn.

Etymology: < Irish sean nós old custom (early 19th cent. or earlier), also specifically denoting styles of traditional musical entertainment (late 19th cent. or earlier, usually with the definite article) < sean old (Early Irish sen : see senior adj.) + nós custom, manner, style (Early Irish nós ), of uncertain origin, perhaps related to the Celtic base of Early Irish, Irish gnás custom, practice, Welsh naws , †gnaws nature, disposition, itself ultimately < the same Indo-European base as know v.The English use as modifier, as seen in sean nós singing, is not paralleled in Irish; compare e.g. Irish amhrán ar an sean nós, literally ‘song in the old style’ (expressing the same concept). Parallel in Scotland. Since the second half of the 20th cent., the equivalent Scottish Gaelic expression seann-nòs (18th cent. or earlier in general use) has also been used with reference to a style of singing (on the model of the Irish use), and is hence also occasionally found in English contexts.