• 海底かいてい — ocean floor
• 心底しんそこ — from the bottom of one’s heart
• 底力そこぢから — hidden strength
• 徹底てってい — thoroughness
• 底辺ていへん — base (of a triangle, or society)
• 湖底こてい — lake bottom
• 眼底がんてい — fundus of the eye

底 captures both the physical bottom and metaphorical depths — such as the base of a container, the lowest point in life, or the true feeling within someone.

The character includes the shelter radical 广, perhaps evoking the idea of a covered base or deep place beneath a surface.

コップの底そこに 砂すなが 沈しずんでいる。
Sand has settled at the bottom of the glass.

彼かれの 心こころの底そこには 優やさしさがある。
There is kindness deep in his heart.

The kun-yomi そこ refers to a literal or metaphorical “bottom.” On-yomi テイ is used in compound words like 徹底 and 心底.