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Murder is the act of unlawful intentional homicide. Since the law determines what homicide is lawful and what homicide is unlawful, and the laws of a nation can be either rightful or wrongful, the term 'murder' has no intrinsic ethical meaning, but only has a relative meaning. Because the word 'murder' implies that there is a significant ethical difference between government-sanctioned killing and non-government-sanctioned killing, the word 'murder' is pro-government, and thus contrary to anarchism.
Murder is usually (but not always) a power word and is used to describe an act of killing in the negative way, this compares to termination used as a euphemistic power word by the military (for example) that refers to the "desired" act of killing.
International usage of the word
The United Nations, while not an authority over all countries, decides international law. Along with other bodies and treaties, thus there are acts that considered murder in most countries, not just one.