eş: земля, суша, купол неба, небо, твердыня, твёрдость
köken: Inherited from Old East Slavic твьрдь (tvĭrdĭ), from Proto-Slavic *tvьrdь. Cognate with Old Church Slavonic тврьдь (tvrĭdĭ, “citadel, base, firmament”) and archaic Bulgarian твърд (tvǎrd, “earth, sky, citadel, firmament”). Compare also твёрдый (tvjórdyj, “hard, firm”).