The realm of science.
An example of a realm is a kingdom in a computer game.
The realm of thought.
An example of a realm is the general way to speak about a subject like science.
An example of a realm is a geographical division of the earth.
Origin of realm
- Middle English realme from Old French alteration (influenced by Old French reial royal) of Latin regimen government from regere to rule reg- in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition