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base (logarithmic, exponential, number system); radix
base (triangle, cone, cylinder, etc.)
type; kind; extent; degree
鍋の底が焦げてしまったんだ。
The bottom of the pot got burnt.
三角形の面積は底の長さと高さを掛け、それを二で割って求める。
The area of a triangle is found by multiplying the length of the base by the height and dividing by two.
川の底が見えるくらい透明だよ。
It's so clear you can see the river bottom.