Cassia comes from the Latin (and Greek kasía) name for the cinnamon tree — a fragrant spice tree whose bark and oil have been valued since antiquity. The Hebrew Keziah (Job 42:14) — one of Job's daughters — shares the same root.
Cassia is rising fast in the U.S. as part of the broader return of botanical and biblical names. The character Cassia in Ally Condie's Matched trilogy gave the name YA visibility.
Cassia reduces to eight — the number of spiced authority.