A merge between: * Proto-Slavic *tъčьnъ (“acute, punctual”) (from the root of тъка́ (tǎká, “to thread”), то́ча (tóča, “to whet, to sharpen”)), which is formally expected to yield **тъчен; * Proto-Slavic *točьnъ (“sprung, derivant”) (from the root of то́ча (tóča, “to drain”), ток (tok, “current”)). The semantics of the modern term has been explicated with the advent of scientific rigour.