Where does “sythyn” come from?

sythyn (Middle English) comes from Old English siþþan, from Old English sīþ, from Proto-West Germanic sinþ, from Proto-Germanic sinþaz, from Proto-Indo-European sent-, from Proto-Indo-European h₁es- — to be.

Ancestry of “sythyn”, step by step

StepLanguageWordMeaning
1Old Englishsiþþanafterwards, subsequently; since; ago, since
2Old Englishsīþjourney, movement, trip, point in time, occasion;...
3Proto-West Germanicsinþjourney, way, path; time, occasion
4Proto-Germanicsinþazjourney, way, path
5Proto-Indo-Europeansent-to head for, to go, to travel; to feel
6Proto-Indo-Europeanh₁es-to be
Every word from Proto-Indo-European h₁es-Every word from Proto-Indo-European sent-Every word from Proto-Germanic sinþaz