means A sudden, powerful discharge of static electricity between clouds or between a cloud and the ground, seen as a brilliant flash of light.

from Straight from Old English 'lihting,' meaning a making-bright or flashing — a verbal noun built on 'lihtan,' 'to make light, to shine.' It shares its glowing root with 'light' itself (Old English 'leoht'), tracing back to the Proto-Indo-European '*leuk-,' a brightness-word that also lit up Latin 'lux' and Greek 'leukos' (white). So the bolt is, quite literally, the sky 'lightening.'