The Greek verb apokteinō means to kill, to slay, to put to death. It is the most common NT verb for killing, used of physical death, martyrdom, spiritual death (killing 'with the sword of the mouth'), and the death of Christ.
The pattern of apokteinō in the Gospels builds toward a devastating climax. Jesus predicts that the Son of Man will be killed (Mark 8:31; 9:31; 10:34) — each prediction more explicit than the last. The Parable of the Tenants (Matthew 21:39) dramatizes Israel's history: the landowner sends servants (the prophets), and they are killed (apokteinō); finally he sends his son, and they kill him too. Jesus also expands the definition of killing in Matthew 5:21-22 — the 'murder' of the sixth commandment includes anger and contempt. Revelation uses apokteinō for both martyrdom (6:11; 13:15) and Christ's judgment (19:21). Death is real in Scripture — but not final: the One who was apoktantheis (killed) is now risen.