sith (adv., conj., prep.) Look up sith at Dictionary.com
"since" (obsolete), Middle English, reduced from Old English siððan "then, thereupon; continuously, during which; seeing that," from *sið þon "subsequent to that," from sið "after," from Proto-Germanic *sith- "later, after" (cognates: Old Saxon sith "after that, since, later," German seit "since," Gothic seiþus "late"), from PIE *se- (2) "long, late" (see soiree).