• 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 expresses both the physical bottom and metaphorical depths — the base of objects, the lowest point in life, or the true core of feelings.

The radical 广 (まだれ) suggests a covered or structural element, reinforcing the sense of foundation or underlying depth.