The origin of flash and flashing are uncertain,[REF] but may come from the Middle English verb flasshen, 'to sprinkle, splash', related to flask [REF].
Counter-flashing (or cover flashing, cap flashing) is a term used when there are two parallel pieces of flashing employed together[REF] such as on a chimney, where the counter-flashing is built into the chimney and overlaps a replaceable piece of base flashing.