Where does “сила” come from?

сила (Old East Slavic) comes from Proto-Slavic sila, from Proto-Balto-Slavic séiˀlāˀ, from Proto-Indo-European seh₂i-l-eh₂, from Proto-Indo-European sh₂ey-, from Proto-Indo-European seh₂- — to satiate, satisfy.

Ancestry of “сила”, step by step

StepLanguageWordMeaning
1Proto-Slavicsilastrength, force
2Proto-Balto-Slavicséiˀlāˀstrength, force; soul
3Proto-Indo-Europeanseh₂i-l-eh₂
4Proto-Indo-Europeansh₂ey-to bind, fetter
5Proto-Indo-Europeanseh₂-to satiate, satisfy
Every word from Proto-Indo-European seh₂-Every word from Proto-Indo-European sh₂ey-Every word from Proto-Indo-European seh₂i-l-eh₂