Fetching details from the dictionary...

origin; source; beginning
basis; base; foundation; root
cause
(raw) material; ingredient; base; mix (e.g. for a cake); (soup) stock
(one's) side
capital; principal; cost price
root (of a plant); (tree) trunk
part (of a brush, chopsticks, etc.) one holds (with the hand)
counter for plants or trees
first three lines of a waka
counter for falcons (in falconry)
元をたどれば彼が原因だ。
If you trace back to the origin, he is the cause.
木の元に座って休んだ。
I sat down at the base of a tree and rested.
この問題のもとになった出来事について調べている。
I'm investigating the event that was the source of this problem.