1bottom; base
2background; foundation
3copy (of a manuscript or receipt etc) kept as a record
4(suffix) end of a year or month
5(math.) radix; base (abbr. for 底數|底数)
Examples
tā他cóng从xīn心dǐ底xiào笑le了chū lái出来。
他从心底笑了出来。
He laughed a hearty laugh.
把这里翻个底朝天！
Leave no stone unturned.
那儿的水深到我碰不到底。
The water there was so deep that I could not touch bottom.