The noun homicide means a murder. If you kill another person, you are committing a homicide. The level of the homicide is legally defined as murder if the act was intentional and as manslaughter if it was unintentional.
Remember the meaning of homicide by remembering that cide, from the Latin cida, refers to killing, while the Latin homo means "man.” So homicide means “killing a man.” You can see another example in this quote from Oliver Wendell Holmes: “Life and language are alike sacred. Homicide and verbicide — that is, violent treatment of a word with fatal results to its legitimate meaning, which is its life — are alike forbidden.”