kill, slay, murder, assassinate, dispatch, execute mean to deprive of life.

kill merely states the fact of death caused by an agency in any manner.

slay is a chiefly literary term implying deliberateness and violence but not necessarily motive.

murder specifically implies stealth and motive and premeditation and therefore full moral responsibility.

assassinate applies to deliberate killing openly or secretly often for political motives.

dispatch stresses quickness and directness in putting to death.

execute stresses putting to death as a legal penalty.