Definition from Wiktionary, the free dictionary
Back-formation from Old Irish fiur, phiur, lenited form of siur (s > f is the regular lenition for words starting with *sw- in Primitive Irish), from Proto-Celtic *swesūr, from Proto-Indo-European *swésōr.
Terms derived from piuthar
|Scottish Gaelic mutation|
|Note: Some of these forms may be hypothetical. Not every
possible mutated form of every word actually occurs.