Solution

WORLDS

3 clues

Planets

Word class: Common noun
Nature of clue: Synonym
Difficulty: Very easy
Sources: Boatload Puzzles
Topics: Space, Universe

Realms

Word class: Common noun
Nature of clue: Synonym
Difficulty: Easy
Sources: Boatload Puzzles
Topics: Geography

Other solutions to Realms

Spheres

Word class: Common noun
Nature of clue: Synonym
Difficulty: Easy
Sources: Boatload Puzzles
Topics: Space, Universe

Other solutions to Spheres

Words are categorized by artificial intelligence: there can be mistakes.