Edward Coke, in his Coke's Institutes (1628, Part III, Chapter 7, page 47):
"Murder is when a man of sound memory and of the age of discretion, unlawfully killeth within any county of the realm any reasonable creature in rerum natura under the king's peace, with malice aforethought, either expressed by the party or implied by law…"
The 2000 edition of Archbold's Criminal Pleading, Evidence and Practice:
"Subject to three exceptions ( provocation, diminished responsibility and action in pursuance of a suicide pact), the crime of murder is committed where a person of sound mind and discretion unlawfully kills any reasonable creature in being and under the Queen's peace with intent to kill or cause grievous bodily harm."
The US Code, at Title 18, defines murder as:
"Murder is the unlawful killing of a human being with malice aforethought."
It has been, since its conception as a crime of common law , evolved to a variety of forms related to intent and planning, such that one no longer hears lawyers or judges speak of murder anymore but, instead, of homicide, of murder specified by degree, or of manslaughter.
However, the Criminal Code of Canada, at ¶229, does define "culpable homicide" as "murder where ...":
"The person who causes the death of a human being means to cause his death, or means to cause him bodily harm that he knows is likely to cause his death, and is reckless whether death ensues or not;
"A person, meaning to cause death to a human being or meaning to cause him bodily harm that he knows is likely to cause his death, and being reckless whether death ensues or not, by accident or mistake causes death to another human being, notwithstanding that he does not mean to cause death or bodily harm to that human being; or
"A person, for an unlawful object, does anything that he knows or ought to know is likely to cause death, and thereby causes death to a human being, notwithstanding that he desires to effect his object without causing death or bodily harm to any human being."
Historically, at common law, Russell on the Law of Crimes gives this definition:
"Murder is the unlawful killing, by any person of sound memory and discretion, of any person under the King's peace, with malice aforethought either express or implied by law.
"This malice aforethought which distinguishes murder from other species of homicide is not limited to particular illwill against the person slain, but means that the fact has been attended with such circumstances as are the ordinary symptoms of a wicked, depraved and malignant spirit; a heart regardless of social duty and deliberately bent upon mischief."
Blackstone in his 1769 Commentaries used these words:
"And if one intends to do another felony, and undesignedly kills a man, this is also murder.
"Thus, if one shoots at A. and misses him, but kills B., this is murder, because of the previous felonious intent, which the law transfers from one to the other."
As late as 1918, the common law was stated as follows in Archbold's Criminal Pleading, Evidence and Practice, 25th Edition:
"If a person, whilst doing or attempting to do another act, undesignedly kills a man -- if the act intended or attempted were a felony, the killing is murder; if unlawful, but not amounting to felony, the killing is manslaughter."
See also the more extensive article in the Criminal Law ? Legal Resource, entitled "Murder!".