Where does “Kostian” come from?

Kostian (Finnish) comes from Finnish konstantin, from Latin Constantinus, from Latin -īnus, from Proto-Italic -īnos, from Proto-Indo-European -iHnos, from Proto-Indo-European -no- — adjectival suffix.

Ancestry of “Kostian”, step by step

StepLanguageWordMeaning
1FinnishkonstantinGenitive singular form of konstantti
2LatinConstantinus
3Latin-īnusof or pertaining to; -ine
4Proto-Italic-īnosof/belonging to
5Proto-Indo-European-iHnosCreates adjectives of materials
6Proto-Indo-European-no-adjectival suffix
Every word from Proto-Indo-European -no-Every word from Latin -īnusEvery word from Proto-Italic -īnos