Where does “оқасы” come from?

оқасы (Kazakh) comes from Bashkir -сы, from Proto-Turkic -či — Profession suffix.

Ancestry of “оқасы”, step by step

StepLanguageWordMeaning
1Bashkir-сыperson who does an action indicated by the root...
2Proto-Turkic-čiProfession suffix
Every word from Proto-Turkic -či →Every word from Bashkir -сы →