The Collaborative International Dictionary of English v.0.48:

Maranta \Ma*ran"ta\, prop. n. [NL.] (Bot.)
   A genus of endogenous plants found in tropical America, and
   some species also in India. They have tuberous roots
   containing a large amount of starch, and from one species
   (Maranta arundinacea, the American arrowroot or obedience
   plant) arrowroot (arrowroot starch) is obtained. Many
   kinds are cultivated for ornament.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Arrowroot \Ar"row*root`\, n.
   1. (Bot.) A white-flowered west Indian plant of the genus
      Maranta, esp. Maranta arundinacea, now cultivated in
      many hot countries. Its root yields arrowroot starch. It
      said that the Indians used the roots to neutralize the
      venom in wounds made by poisoned arrows.

   Syn: arrowroot, American arrowroot, obedience plant.
        [1913 Webster]

   2. A nutritive starch obtained from the rootstocks of
      Maranta arundinacea, and used as food, esp. for children
      an invalids; also, a similar starch obtained from other
      plants, as various species of Maranta and Curcuma.
      [1913 Webster]

WordNet (r) 3.0 (2006):

arrowroot
    n 1: a nutritive starch obtained from the root of the arrowroot
         plant
    2: white-flowered West Indian plant whose root yields arrowroot
       starch [syn: arrowroot, American arrowroot, obedience
       plant, Maranta arundinaceae]
    3: canna grown especially for its edible rootstock from which
       arrowroot starch is obtained [syn: achira, indian shot,
       arrowroot, Canna indica, Canna edulis]