Where does “sitkeytyä” come from?

sitkeytyä (Finnish) comes from Finnish -utua, from Finnish -ua, from Proto-Finnic -üdäk — Forms mainly passive or anticausative verbs.

Ancestry of “sitkeytyä”, step by step

StepLanguageWordMeaning
1Finnish-utua—
2Finnish-uaForms stative or inchoative intransitive verbs...
3Proto-Finnic-üdäkForms mainly passive or anticausative verbs
Every word from Proto-Finnic -üdäk →Every word from Finnish -ua →Every word from Finnish -utua →