flash: [14] The earliest recorded use of flash is as a verb, referring to the swift turbulent splashing movement of water (a memory of which is probably preserved in modern English flash flood). The glints of light on the splashing surface of such water seems to have given rise in the 16th century, or perhaps before, to the main present-day sense of the word ‘burst out with sudden light’. It was presumably originally imitative of the sound of splashing water. [flash etymology, flash origin, 英语词源]