The Greek verb sphazo (σφάζω) means to slay by cutting the throat — the killing method used in animal sacrifice and violent death. It appears 10 times in the NT, mostly in Revelation. It is a vivid, visceral word.
Sphazo connects the sacrificial system to the cross in striking ways. Revelation 5:6 depicts the Lamb 'standing as though it had been slain (esphagmenon)' — Jesus bears the marks of His slaughter even in glory. Revelation 5:9, 12 proclaim: 'You were slain, and with your blood you purchased for God persons from every tribe.' The Lamb's slaughter is the axis of heaven's worship. First John 3:12 uses sphazo for Cain's murder of Abel — the first martyr blood. Revelation 6:9 shows the souls of those slain because of the word of God under the altar — martyrs in heaven. Sphazo makes the blood of the covenant visible and costly.