1. murder – 故意杀人，即谋杀。它专指“有预谋的蓄意谋杀”，区别于manslaughter‘误杀’。
Murder, as defined in common law countries, is the unlawful killing of another human being with intent (or malice aforethought), and generally this state of mind distinguishes murder from other forms of unlawful homicide (such as manslaughter).
2. manslaughter 指“过失杀人”或“误杀”，着重于没有预谋的杀人。所以，非自愿的杀人，被称为 involuntary manslaughter。甚至，即使是有意的杀人行为：，但显然具有从轻情节的，比如遇到对方挑衅、出于职务上的原因、或者出于正当防卫的杀人，也称 voluntary manslaughter，而不用murder这个词。
Manslaughter is a legal term for the killing of a human being, in a manner considered by law as less culpable（意图） than murder.
The law generally differentiates between levels of criminal culpability based on the mens rea（犯罪意图）, or state of mind. This is particularly true within the law of homicide, where murder requires either the intent to kill, a state of mind called malice, or malice aforethought（预谋）, which may involve an unintentional killing but with a wilful disregard for life. Manslaughter is usually broken down into two distinct categories: voluntary manslaughter and involuntary manslaughter.
3. homicide – 则泛指所有的杀人，既包括意外的过失杀人，也包括故意杀人。如 The homicide rate has doubled in the last five years.(在过去五年中，杀人犯罪率增加了一倍。)这显然指各种各样的杀人案件。如culpable homieide (刑事杀人)，justifiable homicide (正当杀人)等都包括在内。
Homicide (Latin: homicidium, Latin: homo human being + Latin: caedere to cut, kill) refers to the act of a human killing a human being. A common form of homicide, for example, would be murder. It can also describe a person who has committed such an act, though this use is rare in modern English. Homicide is not always an illegal act, so although “homicide” is often used as a synonym for “murder”, this is not formally correct.