Definitions of Mo:

• noun:   a polyvalent metallic element that resembles chromium and tungsten in its properties; used to strengthen and harden steel
• noun:   a midwestern state in central United States; a border state during the American Civil War, Missouri was admitted to the Confederacy without actually seceding from the Union
• name:  A surname (rare: 1 in 100000 families; popularity rank in the U.S.: #16063)