• 世界せかい — the world
• 限界げんかい — limit / boundary
• 業界ぎょうかい — industry / business world
• 政界せいかい — political world
• 学界がっかい — academic circles
• 視界しかい — field of vision / visibility
• 世界中せかいじゅう — all over the world

界 combines the element 田 (rice field) with 介 (to intervene), evoking boundaries between fields. By extension, it came to mean broader “spheres” or “realms,” such as the world (世界) or professional fields (業界).