To kill vs. to murder
To kill is to deprive of life; may refer not only to a person (e.g., to kill a plant);
to murder implies the crime of unlawfully killing a person especially with malice aforethought.
In terms of deprivation of life there are also terms "to assassinate" and "to slay". To assassinate is to commit a political murder. The victim in this case is someone with whose views the assassin does not agree and he kills him to rid the world of someone whom he perceives as a threat to its wellbeing. To slay is old-fashioned word for "to kill", but with additional meaning to kill with an object.