full article and abstract in Lithuanian; abstract in English The present paper consists of two parts. The first one is dedicated to the etymology of the Lithuanian noun perkūnas (“thunder, thunderbolt”). According to the author, perkūnas is a derivative with a possessive suffix -Hon- / -Hn from the IDE *perkwu-s (“oak”). The second part concerns the origin of the Lithuanian aitvaras (“supernatural being,” OLith. aitvaras). The analyzed noun is an instance of the so-called Caland system in the Baltic languages, and it traces back to the older compound word with the meaning *“being bestowed with flaming power.” straipsnis ir santrauka lietuvių kalba; santrauka anglų kalba Straipsnyje aptariamos perkūno ir aitvaro (slie. aitivaro) etimologijos. Abu daiktavardžiai vertinami kaip naujadarai, bet abiejų žodžių daryba pagrįsta iš ide. prokalbės paveldėtais darybiniais procesais.