1. A political or territorial unit ruled by a sovereign.

3. A realm or sphere in which one thing is dominant: the kingdom of the imagination.

4. In the Linnean taxonomic system, the highest taxonomic category into which organisms are grouped, based on fundamental similarities and common ancestry. One widely used taxonomic system designates five or six such groups: animals, plants, fungi, protists, and prokaryotes (often divided into bacteria and archaea). Other systems divide organisms into domains (eukaryotes, bacteria, and archaea) that replace or rank above kingdoms.

5. One of the three main divisions (animal, vegetable, and mineral) into which natural organisms and objects have traditionally been classified.