Murder n. is most prominently defined as the deliberate and unlawful killing of another human being. It is in this distinction that the line between murder and killing is drawn. Of course inevitably murder involves killing but killing covers a wider range of action including the death of animals. The unlawful part of the definition distinguishes it from the facilitation of deaths within the boundaries of the law such as executions or killing during war. Murder can also be in the form of a verb, the act of committing the above, and as another noun, a flock of crows. Murder has a common origin with the Gothic maurþr, a word of Indo-European base which branches out to form morth, mr, morti and mort all staying very close to the meaning of death, dying and mortality. In West Germanic languages the word murder the noun is not found but the verb and murther, a noun meaning a murderer or assassin, are.
The specifics of the laws’ definition of murder has varied over time though always involving the uncondoned killing of another human being. Britton says that murder is only committed if the two involved are unidentified and the ‘deliberate’ part of the definition, in current legal terms, malice aforethought, does not come up until the Homicide Act of 1957. In the Homicide Act one could also be guilty of ‘wilful murder’ if the intention was not to kill but just harm the victim and from then on murder has usually included a death resulting from the desire to inflict harm. This death may only occur within one year and one day after the act was committed, otherwise it would be too possible for other factors to have been the cause, for it to be defined as murder. In many legal systems murder is divided into two or three degrees. There is murder of the first degree which means there was premeditation, murder of the second degree is one committed in the spur of the moment with no prior intentions and third degree murder, when called that is similar to manslaughter.
Murder the verb and the flock of crows likely had the same origins as the most commonly used noun. The use of it as a name for a flock of crows is probably a result of the association of crows with foreshadowing death or bad luck. Murder can be described in terms of the law, refer to sin, be personified and even be used hyperbolically, but its definition has never strayed from death and dying.
 Oxford English Dictionary, "murder (n)." Last modified 2003. Accessed November 21, 2012. http://www.oed.com/view/Entry/123858?rskey=9vjy7y&result=1&isAdvanced=false
 Oxford English Dictionary, "morth (n)." Last modified 2002. Accessed November 21, 2012. http://www.oed.com/view/Entry/123967