Where does “eyeth” come from?

eyeth (English) comes from English Eye, from English -some, from Middle English -som, from Old English sum, from Proto-West Germanic *sum, from Proto-Germanic sumaz, from Proto-Indo-European sem- — together, one.

Ancestry of “eyeth”, step by step

eyeth traces back through two separate lines of ancestry.

via English Eye

StepLanguageWordMeaning
1EnglishEyeA place name
2English-someCharacterized by some specific condition or...
3Middle English-somsome; having a specific quality
4Old Englishsumsome
5Proto-West Germanic*sumsome
6Proto-Germanicsumazsome (one), a certain (one)
7Proto-Indo-Europeansem-together, one

via English eth

StepLanguageWordMeaning
1EnglishethA letter introduced into Old English to...
Every word from Proto-Indo-European sem-Every word from Proto-Germanic sumazEvery word from Proto-West Germanic *sum