Where does “wrth hyn” come from?

wrth hyn (Welsh) comes from Welsh hyn, from Middle Welsh hynn, from Old Welsh hinn, from Proto-Celtic sindos, from Proto-Indo-European sḗm, from Proto-Indo-European sem- — together, one.

Ancestry of “wrth hyn”, step by step

wrth hyn traces back through two separate lines of ancestry.

via Welsh hyn

StepLanguageWordMeaning
1Welshhynin conjunction with the definite article these
2Middle Welshhynn—
3Old Welshhinn—
4Proto-Celticsindosthis
5Proto-Indo-Europeansḗmone
6Proto-Indo-Europeansem-together, one

via Welsh wrth

StepLanguageWordMeaning
1Welshwrthby; as, while
2Old Welshgurt—
3Proto-Celticwrit-against, opposite
4Proto-Indo-Europeanwert-to turn, to rotate
5Proto-Indo-Europeanwer-to burn; to cover, heed, notice; squirrel
Every word from Proto-Indo-European sem- →Every word from Proto-Indo-European sḗm →Every word from Proto-Celtic sindos →