Where does “sulkeutuma” come from?

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

Ancestry of “sulkeutuma”, step by step

Step	Language	Word	Meaning
1	Finnish	sulkeutua	to close oneself in, to shut oneself in
2	Finnish	-utua	—
3	Finnish	-ua	Forms stative or inchoative intransitive verbs...
4	Proto-Finnic	-üdäk	Forms mainly passive or anticausative verbs

Every word from Proto-Finnic -üdäk →Every word from Finnish -ua →Every word from Finnish -utua →