Where does “ættern” come from?

ættern (Old English) comes from Proto-West Germanic ait(t)rīn, from Proto-West Germanic -īn, from Proto-Germanic -īnaz, from Proto-Indo-European -iHnos, from Proto-Indo-European -no- — adjectival suffix.

Ancestry of “ættern”, step by step

StepLanguageWordMeaning
1Proto-West Germanicait(t)rīnpoisonous
2Proto-West Germanic-īnCreates adjectives from nouns with the sense...
3Proto-Germanic-īnaz-en
4Proto-Indo-European-iHnosCreates adjectives of materials
5Proto-Indo-European-no-adjectival suffix
Every word from Proto-Indo-European -no- →Every word from Proto-Germanic -īnaz →Every word from Proto-West Germanic -īn →