taproot

from WordNet (r) 3.0 (2006)

taproot
    n 1: (botany) main root of a plant growing straight downward
         from the stem
    2: something that provides an important central source for
       growth or development; "the taproot of his resentment";
       "genius and insanity spring from the same taproot"

from The Collaborative International Dictionary of English v.0.48

Taproot \Tap"root`\, n. (Bot.)
   The root of a plant which penetrates the earth directly
   downward to a considerable depth without dividing.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

28 Moby Thesaurus words for "taproot":
      beginning, bulb, bulbil, commencement, conception, corm,
      derivation, genesis, grass roots, head, inception, origin,
      original, origination, provenience, radical, radicle, radix,
      rhizome, rise, root, rootstock, source, stem, stock, tap, tuber,
      tubercle

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