From Old High German sint. The onset z- is probably from prepositioned ze (“to”) as in cognate Dutch sinds (from earlier *t(e)zinds). More distant cognates include German seit and English since.
zanter (+ dative)
- since (a point in time)
- Ech wunnen hei zanter dem leschte Joer.
- I've lived here since last year.
- for (a time span)
- Ech wunnen hei zanter engem Joer.
- I've lived here for a year.