Where does “светлячок” come from?

светлячок (Russian) comes from Russian светля́к, from Russian све́тлый, from Proto-Slavic světьlъ, from Proto-Slavic světъ, from Proto-Balto-Slavic śwaitas, from Proto-Indo-European ḱweyt- — to shine.

Ancestry of “светлячок”, step by step

StepLanguageWordMeaning
1Russianсветля́кglowworm; firefly, lightning bug
2Russianсве́тлыйlight
3Proto-Slavicsvětьlъbright
4Proto-Slavicsvětъlight; world
5Proto-Balto-Slavicśwaitas—
6Proto-Indo-Europeanḱweyt-to shine
Every word from Proto-Indo-European ḱweyt- →Every word from Proto-Balto-Slavic śwaitas →Every word from Proto-Slavic světъ →