Beltane or Beltaine (origin Old Irish) is the anglicised spelling of Bealtaine or Bealltainn the Gaelic names for either the month of May or the festival that takes place on the first day of May. However it officially begins at moonrise on May Day Eve.
In Irish Gaelic, the month of May is known as Mí Bhealtaine or Bealtaine, and the festival as Lá Bealtaine ('day of Bealtaine' or, 'May Day'). In Scottish Gaelic, the month is known as either (An) Cèitean or a' Mhàigh, and the festival is known as Latha Bealltainn or simply Bealltainn. The feast was also known as Céad Shamhain or Cétshamhainin from which the word Céitean derives.
As an ancient Gaelic festival, Bealtaine was celebrated in Ireland, Scotland and the Isle of Man, though there were similar festivals held at the same time in the other Celtic countries of Wales, Brittany and Cornwall. Bealtaine and Samhain were the leading terminal dates of the civil year in Ireland though the latter festival was the more important. The festival survives in folkloric practices in the Celtic Nations and the Irish diaspora, and has experienced a degree of revival in recent decades.
The word Beltane derives directly from the Old Irish Beltain, which later evolved into the Modern Irish Bealtaine. In Scottish Gaelic it is spelled Bealltainn. Both are from Old Irish Beltene ('bright fire') from belo-te(p)niâ. Beltane was formerly spelled 'Bealtuinn' in Scottish Gaelic; in Manx it is spelt 'Boaltinn' or 'Boaldyn'.
In Modern Irish, Oidhche Bealtaine or Oíche Bealtaine is May Eve, and Lá Bealtaine is May Day. Mí na Bealtaine, or simply Bealtaine is the name of the month of May.