noun: (astronomy, meteorology) an upper atmospheric optical phenomenon associated with thunderstorms, rapidly expanding disk-shaped regions of luminosity, lasting less than a thousandth of a second, which occur high above energetic cloud-to-ground lightning of positive or negative polarity
noun: Obsolete form of elf. [(Norse mythology) A luminous spirit presiding over nature and fertility and dwelling in the world of Álfheim (Elfland). Compare angel, nymph, fairy.]
