What is a festival of the heathen Celts on the first day of May, in the observance of which great bonfires were kindled. It still exists in a modified form in some parts of Scotland and Ireland called?

beltane — A festival of the heathen Celts on the first day of May, in the observance of which great bonfires were kindled. It still exists in a modified form in some parts of Scotland and Ireland. (Webster's 1913.)

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