Where does “rei'ikäs” come from?

rei'ikäs (Finnish) comes from Finnish -käs, from Proto-Finnic -k'as, from Proto-Finnic -s, from Proto-Finno-Ugric -s.

Ancestry of “rei'ikäs”, step by step

StepLanguageWordMeaning
1Finnish-käsFront vowel variant of -kas
2Proto-Finnic-k'asForms adjectives from nouns, indicating a...
3Proto-Finnic-sForms nouns
4Proto-Finno-Ugric-s—
Every word from Proto-Finno-Ugric -s →Every word from Finnish -käs →Every word from Proto-Finnic -s →