Where does “судейский” come from?

судейский (Russian) comes from Russian судья́, from Proto-Slavic sǫdì, from Proto-Indo-European som-dʰh₁-ih₁.

судейский (Russian): judicial; referee's, umpire's; officer of the...

Definitions

Step	Language	Word	Meaning
1	Russian	судья́	—
2	Proto-Slavic	sǫdì	judge
3	Proto-Indo-European	som-dʰh₁-ih₁	—

судейский — Etymology, Origin & Word History | Etymology Explorer