A murder is the unlawful killing of another human without justification or valid excuse, especially the unlawful killing of another human being with malice aforethought. This state of mind may, depending upon the jurisdiction, distinguish murder from other forms of unlawful homicide, such as manslaughter. Manslaughter is a killing committed in the absence of malice, brought about by reasonable provocation, or diminished capacity. Involuntary manslaughter, where it is recognized, is a killing that lacks all but the most attenuated guilty intent (mens rea), recklessness.
Most societies consider murder to be a very serious crime, and thus believe that the person charged should receive harsh punishments for the purposes of retribution, deterrence, rehabilitation, or incapacitation. In most countries, a person convicted of murder generally faces a long-term prison sentence, possibly a life sentence where permitted.
In many common law jurisdictions, a person convicted of murder will receive a mandatory life sentence. In jurisdictions where capital punishment exists, the death penalty may be imposed for such an act; however, this practice is now less common.
The modern English word "murder" descends from the Proto-Indo-European "mrtró" which meant "to die". The Middle English mordre is a noun from Anglo-Saxon morðor and Old French murdre. Middle English mordre is a verb from Anglo-Saxon myrdrian and the Middle English noun.