Where does “-in” come from?

-in (Proto-Brythonic) comes from Proto-Celtic -īnos, from Proto-Indo-European -iHnos, from Proto-Indo-European -no- — adjectival suffix.

Ancestry of “-in”, step by step

StepLanguageWordMeaning
1Proto-Celtic-īnosOf or pertaining to; -ine
2Proto-Indo-European-iHnosCreates adjectives of materials
3Proto-Indo-European-no-adjectival suffix

Words derived from “-in”

Every word from Proto-Indo-European -no- →Every word from Proto-Celtic -īnos →Every word from Proto-Indo-European -iHnos →