Where does “тысячелетний” come from?

тысячелетний (Russian) comes from Russian ты́сяча, from Old East Slavic тысяча, from Proto-Slavic tỳsęti, from Proto-Balto-Slavic *tū́ˀsantis, from Proto-Indo-European tuHsont-, from Proto-Indo-European tewh₂- — to swell; to crowd; to be strong.

тысячелетний (Russian): thousand-year; thousand-year-old

Definitions

  1. thousand-year; thousand-year-old

Ancestry of “тысячелетний”, step by step

тысячелетний traces back through two separate lines of ancestry.

via Russian ты́сяча

StepLanguageWordMeaning
1Russianты́сячаthousand
2Old East Slavicтысяча—
3Proto-Slavictỳsęti—
4Proto-Balto-Slavic*tū́ˀsantisthousand
5Proto-Indo-EuropeantuHsont-thousand
6Proto-Indo-Europeantewh₂-to swell; to crowd; to be strong

via Russian ле́то

StepLanguageWordMeaning
1Russianле́тоyear; summer, year
2Old East Slavicлѣтоtime
3Proto-Slaviclětosummer; year
4Proto-Indo-Europeanleh₁tóm—
Every word from Proto-Indo-European tewh₂- →Every word from Proto-Indo-European tuHsont- →Every word from Proto-Balto-Slavic *tū́ˀsantis →