Webster's Revised Unabridged Dictionary · 1913

Sith

Sith , prep., adv., & conj.

[See Since.]

Since; afterwards; seeing that. [Obsolete]
We need not fear them, sith Christ is with us. — Latimer
Sith thou art rightful judge. — Chaucer

Sith , noun

[Anglo-Saxon {not transcribed} a path, way, time, occasion.]

Time. [Obsolete] — Chaucer
And humbly thanked him a thousand sithes. — Spenser

Also: Sithe