- since (adv.)
- mid-15c., synnes, from sithenes "since," from sithen (plus adverbial genitive -es), from Old English siððan "then, later, after that," originally sið ðan "after that," from sið "after" + ðan, weakened form of ðam, dative of ðæt (see that).
Modern spelling replaced syns, synnes 16c. to indicate voiceless final -s- sound. Old English sið is from PIE *se- "long, late" (see soiree).