Where does “тьлѣти” come from?

тьлѣти (Old East Slavic) comes from Proto-Slavic tьlěti, from Proto-Balto-Slavic til-.

Ancestry of “тьлѣти”, step by step

StepLanguageWordMeaning
1Proto-Slavictьlětito decay; to smolder
2Proto-Balto-Slavictil-—
Every word from Proto-Balto-Slavic til- →Every word from Proto-Slavic tьlěti →