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2 definitions found
 for Root hair
From The Collaborative International Dictionary of English v.0.48 :

  Root \Root\, n. [Icel. r[=o]t (for vr[=o]t); akin to E. wort,
     and perhaps to root to turn up the earth. See Wort.]
     1. (Bot.)
        (a) The underground portion of a plant, whether a true
            root or a tuber, a bulb or rootstock, as in the
            potato, the onion, or the sweet flag.
        (b) The descending, and commonly branching, axis of a
            plant, increasing in length by growth at its extremity
            only, not divided into joints, leafless and without
            buds, and having for its offices to fix the plant in
            the earth, to supply it with moisture and soluble
            matters, and sometimes to serve as a reservoir of
            nutriment for future growth. A true root, however, may
            never reach the ground, but may be attached to a wall,
            etc., as in the ivy, or may hang loosely in the air,
            as in some epiphytic orchids.
            [1913 Webster]
  
     2. An edible or esculent root, especially of such plants as
        produce a single root, as the beet, carrot, etc.; as, the
        root crop.
        [1913 Webster]
  
     3. That which resembles a root in position or function, esp.
        as a source of nourishment or support; that from which
        anything proceeds as if by growth or development; as, the
        root of a tooth, a nail, a cancer, and the like.
        Specifically:
        (a) An ancestor or progenitor; and hence, an early race; a
            stem.
            [1913 Webster]
  
                  They were the roots out of which sprang two
                  distinct people.                  --Locke.
            [1913 Webster]
        (b) A primitive form of speech; one of the earliest terms
            employed in language; a word from which other words
            are formed; a radix, or radical.
        (c) The cause or occasion by which anything is brought
            about; the source. "She herself . . . is root of
            bounty." --Chaucer.
            [1913 Webster]
  
                  The love of money is a root of all kinds of
                  evil.                             --1 Tim. vi.
                                                    10 (rev. Ver.)
            [1913 Webster]
        (d) (Math.) That factor of a quantity which when
            multiplied into itself will produce that quantity;
            thus, 3 is a root of 9, because 3 multiplied into
            itself produces 9; 3 is the cube root of 27.
        (e) (Mus.) The fundamental tone of any chord; the tone
            from whose harmonics, or overtones, a chord is
            composed. --Busby.
            [1913 Webster]
        (f) The lowest place, position, or part. "Deep to the
            roots of hell." --Milton. "The roots of the
            mountains." --Southey.
            [1913 Webster]
  
     4. (Astrol.) The time which to reckon in making calculations.
        [1913 Webster]
  
              When a root is of a birth yknowe [known]. --Chaucer.
        [1913 Webster]
  
     Aerial roots. (Bot.)
        (a) Small roots emitted from the stem of a plant in the
            open air, which, attaching themselves to the bark of
            trees, etc., serve to support the plant.
        (b) Large roots growing from the stem, etc., which descend
            and establish themselves in the soil. See Illust. of
            Mangrove.
  
     Multiple primary root (Bot.), a name given to the numerous
        roots emitted from the radicle in many plants, as the
        squash.
  
     Primary root (Bot.), the central, first-formed, main root,
        from which the rootlets are given off.
  
     Root and branch, every part; wholly; completely; as, to
        destroy an error root and branch.
  
     Root-and-branch men, radical reformers; -- a designation
        applied to the English Independents (1641). See Citation
        under Radical, n., 2.
  
     Root barnacle (Zool.), one of the Rhizocephala.
  
     Root hair (Bot.), one of the slender, hairlike fibers found
        on the surface of fresh roots. They are prolongations of
        the superficial cells of the root into minute tubes.
        --Gray.
  
     Root leaf (Bot.), a radical leaf. See Radical, a., 3
        (b) .
  
     Root louse (Zool.), any plant louse, or aphid, which lives
        on the roots of plants, as the Phylloxera of the
        grapevine. See Phylloxera.
  
     Root of an equation (Alg.), that value which, substituted
        for the unknown quantity in an equation, satisfies the
        equation.
  
     Root of a nail
        (Anat.), the part of a nail which is covered by the skin.
                
  
     Root of a tooth (Anat.), the part of a tooth contained in
        the socket and consisting of one or more fangs.
  
     Secondary roots (Bot.), roots emitted from any part of the
        plant above the radicle.
  
     To strike root, To take root, to send forth roots; to
        become fixed in the earth, etc., by a root; hence, in
        general, to become planted, fixed, or established; to
        increase and spread; as, an opinion takes root. "The
        bended twigs take root." --Milton.
        [1913 Webster]

From WordNet (r) 3.0 (2006) :

  root hair
      n 1: thin hairlike outgrowth of an epidermal cell just behind
           the tip; absorbs nutrients from the soil

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