Law . the killing of another human being under conditions specifically covered in law. In the U.S., special statutory definitions include murder committed with malice aforethought, characterized by deliberation or premeditation or occurring during the commission of another serious crime, as robbery or arson ( first-degree murder, or murder one ), and murder by intent but without deliberation or premeditation ( second-degree murder, or murder two ).

Slang . something extremely difficult or perilous: That final exam was murder!