зна̑к (Serbo-Croatian) comes from Proto-Slavic znakъ, from Proto-Slavic znati, from Proto-Balto-Slavic źnōˀtei, from Proto-Indo-European ǵnéh₃t, from Proto-Indo-European ǵneh₃- — to know.
зна̑к (Serbo-Croatian): sign