• 階段かいだん — stairs
• 一階いっかい — first floor
• 二階にかい — second floor
• 階級かいきゅう — rank, class
• 階層かいそう — hierarchy, layer
• 階上かいじょう — upper floor

階 combines the hill radical (阝) with the phonetic part 皆 (カイ). Originally related to places on elevated ground, it now mainly expresses levels or steps in both physical and abstract senses.