Where does “myhkyrä” come from?

myhkyrä (Finnish) comes from Finnish -ra, from Finnish -i, from Proto-Uralic -j — oblique plural.

Ancestry of “myhkyrä”, step by step

Step	Language	Word	Meaning
1	Finnish	-ra	Forms nouns or adjectives, mostly from nominal...
2	Finnish	-i	A nominal suffix used in eg. ukko → ukki; Used...
3	Proto-Uralic	-j	oblique plural