realm 
(rĕlm)
(rĕlm)n.
1. A community or territory over which a sovereign rules; a kingdom.
2. An area or sphere, as of knowledge or activity: the realm of science. See Synonyms at field.
[Middle English realme, from Old French, alteration (influenced by Old French reial, royal) of Latin regimen, government, from regere, to rule; see reg- in the Appendix of Indo-European roots.]