from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The main root of a plant, usually stouter than the lateral roots and growing straight downward from the stem.
from the GNU version of the Collaborative International Dictionary of English
- n. The root of a plant which penetrates the earth directly downward to a considerable depth without dividing.
from The Century Dictionary and Cyclopedia
- n. 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.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. something that provides an important central source for growth or development
- n. (botany) main root of a plant growing straight downward from the stem
tap + root (Wiktionary)