Root (noun)

1. The part of a plant that attaches it to the ground or to a support, typically underground, conveying water and nourishment to the rest of the plant via numerous branches and fibers.
2. The fundamental or underlying cause, source, or basis of something.

Origin:

Old english rōt, of germanic origin; related to dutch wortel and german wurzel.

Examples:

1. The plant's roots absorb water and nutrients from the soil.
2. The root of the problem is lack of funding.
3. He traced the root of the word to its Latin origin.
4. The root cause of the disease is still unknown.
5. She found the root of the plant and used it for medicine.