Serbo-Croatian тко

← Proto-Indo-European *kʷos (derived)

← Proto-Indo-European *kʷid (mention)

← Proto-Indo-European *kʷis (mention)

← Proto-Slavic *kъto (inherited)

→ Serbo-Croatian нитко (prefix)

→ Serbo-Croatian итко (prefix)

→ Serbo-Croatian ткогод (suffix)