Where does “-тва” come from?

-тва (Russian) comes from Proto-Slavic -tva, from Proto-Indo-European -tweh₂, from Proto-Indo-European -eh₂.

Ancestry of “-тва”, step by step

Step	Language	Word	Meaning
1	Proto-Slavic	-tva	Deverbative, forming nouns denoting an act,...
2	Proto-Indo-European	-tweh₂	Forms nouns from verbs
3	Proto-Indo-European	-eh₂	—

-тва — Etymology, Origin & Word History | Etymology Explorer