taproot

The main root of a plant, usually stouter than the lateral roots and growing straight downward from the stem.

In botany, the main root of a plant, which grows vigorously downward to a considerable depth, giving off lateral roots in acropetal succession. See cut under root.

The root of a plant which penetrates the earth directly downward to a considerable depth without dividing.

something that provides an important central source for growth or development

(botany) main root of a plant growing straight downward from the stem