flashing (n.) Look up flashing at Dictionary.com
1791, "act of creating an artificial flood," verbal noun from flash (v.); also compare flash (n.2)). Meaning "indecent exposure" is by 1968 (see flasher). The meaning "strip of metal used in roofing, etc." is from 1782, earlier simply flash (1570s), but the sense connection is unclear and it might be an unrelated word.
flashing (adj.) Look up flashing at Dictionary.com
1540s, of light; present participle adjective from flash (v.).