From *tör-üg, from Proto-Turkic *töre- (“to be born, originate”), whence also Turkish türe-. Compare Old Turkic 𐱅𐰇𐰼 (t²ür² /törü/, “custom, law, statute, tradition”).
Compare also Mongolian дүрэм (dürem, “rule”), as well as perhaps Hungarian törvény (“law”), etc.