• 草原そうげん — grassland / prairie
• 湿原しつげん — wetland / marshland
• 原野げんや — wilderness / plain
• 高原こうげん — highland / plateau
• 原はらっぱ — plain / field
• 原因げんいん — cause
• 原点げんてん — starting point
• 原子げんし — atom
• 病原菌びょうげんきん — pathogen / disease-causing germ

原 often points to something “basic” or “at the beginning.” It can describe open land (a plain or field), and it also appears in words for cause, starting point, and origin — like a return to where something began.