root, founded on
柢 centers on the foundational root of a plant, and by extension something that is firmly grounded or based on a solid foundation.
柢 combines 木 (tree/wood) with 氐, which likely contributes the sound and carries a sense of base or foundation, together suggesting the root of a tree.
The tree 木 beside the base 氐: picture the deep root of a tree anchoring it firmly to the ground.
For テイ, imagine a sturdy root shaped like the letter T, firmly planted in the earth: T -> テイ, the root that holds the tree.