Definitions of kingdom:

• noun:   a basic group of natural objects
• noun:   one of seven biological categories: Monera or Protoctista or Plantae or Fungi or Animalia
• noun:   a monarchy with a king or queen as head of state
• noun:   the domain ruled by a king or queen
• noun:   a country with a king as head of state
• noun:   a domain in which something is dominant

  Example: "The untroubled kingdom of reason"

• name:  A surname (very rare: popularity rank in the U.S.: #43274)