1. The killing of a human being with malice aforethought. * At common law, the crime of murder was not subdivided, but many state statutes have adopted the degree structure outlined below, though the Model Penal Code has not. Model Penal Code § 210.2.
See MALICE AFORETHOUGHT. — murder, vb. — murderous, adj. 
A technical term or word of art which can be defined with particularity only by resort to the specific. statute in the jurisdiction involved. Re Kirby, 162 Cal 91, 121 P 370.
At common law, the killing of one human being by another with malice aforethought, either express or implied, that is, with deliberate intent or formed design to kill. 26 Am J1st Homi § 11; Wiley v State, 19 Ariz 346, 170 P 869; Commonwealth v Buzard, 365 Pa 511, 76 AM 394, 22 ALR2d 846.
The intentional killing of a human being without legal justification or excuse and under circumstances insufficient to reduce the crime to manslaughter. 26 Am J1st Homi § 11. 
1. The intentional and premeditated killing of a human being (first degree murder); the intentional killing of a human being, without premeditation, but with malice aforethought, express or implied (second degree murder). Under most state statutes, a homicide that occurs during the commission of a felony is first degree murder, as are homicides perpetrated by ling in wait, torture, poison, and other criminal acts from which premeditation or deliberation can be inferred. Similarly, a homicide that results from deliberately doing a dangerous or deadly act with disregard for the safety of others is second degree murder, malice being inferred from the act itself. 
Excerpt from Theodore F.T. Plucknett’s A Concise History of the Common Law (5th ed. 1956):
“The word ‘murder’ has . . . had a devious history. Its original sense is the particularly heinous crime of secret slaying. After the conquest it was observed that Normans were frequently found dead under mysterious circumstances, and so William I enacted that if anyone were found slain and the slayer were not caught, then the hundred should pay a fine; this fine is a murdrum. The practice soon grew up to taking inquests and if it were presented that the dead man was English, then the fine was not due. In 1267 it was enacted that accidental deaths should not give rise to murdrum, and finally in 1340 presentment of Englishry and murdrum were abolished. Henceforth the word slowly tends to get linked up with ‘malice aforethought’ and so we get the classical formulae describing the crime of murder.” 
Varying Types and Degrees of Murder:
open murder – 1. An unsolved homicide. 2. A charge presenting the elements of both first and second-degree murder. * The jury must decide whether to convict of either first- or second-degree murder (but not both) based on the evidence.
first degree murder – willful, deliberate, or premeditated murder, or murder committed during the course of another dangerous felony. — aka murder of the first degree; murder one.
- felony murder – occurs during the commission of a dangerous felony (often limited to rape, kidnapping, robbery, burglary, and arson). — aka unintentional murder; (in English law) constructive murder.
- felony-murder rule – a death which occurs by accident or chance during the course of the commission of a felony is first degree murder.
- murder by torture – murder preceded by intentional infliction of pain and suffering on the victim.
- mass murder – (1917) A murderous act or series of acts by which a criminal kills many victims at or near the same time, usually as part of one act or plan. Cf. serial murder; MASSACRE.
- serial murder – (1977) A murder in which a criminal kills one of many victims over time, often as part of a pattern in which the criminal targets victims who have some similar characteristics. Cf. mass murder.
- willful murder – (16C) The unlawful and intentional killing of another without excuse or mitigating circumstances.
second degree murder – committed with intent to kill, but not premeditated or deliberate. — aka murder of the second degree; murder two. 
- depraved-heart murder – a mu