błyskać (Old Polish) comes from Serbo-Croatian bliskati, from Serbo-Croatian blijȇsak, from Proto-Slavic blěskъ, from Proto-Balto-Slavic blaiskas, from Proto-Indo-European bʰloyǵskos, from Proto-Indo-European bʰleyǵ- — to shine.
błyskać (Old Polish): to flash