Source : Webster's Revised Unabridged Dictionary (1913)

Sith \Sith\, prep., adv., & conj. [See {Since}.]
   Since; afterwards; seeing that. [Obs.]

         We need not fear them, sith Christ is with us.
                                                  --Latimer.

         Sith thou art rightful judge.            --Chaucer.

Sith \Sith\, Sithe \Sithe\, n. [AS. ??? a path, way, time,
   occasion.]
   Time. [Obs.] --Chaucer.

         And humbly thanked him a thousand sithes. --Spenser.