пълноле́тен (Bulgarian) comes from Bulgarian пълноле́тие, from Bulgarian пълен, from Old Church Slavonic пльнъ, from Proto-Slavic pьlnъ, from Proto-Balto-Slavic pílˀnas, from Proto-Indo-European pl̥h₁nós, from Proto-Indo-European pleh₁- — to fill.
пълноле́тен (Bulgarian): major person of legal age