The Collaborative International Dictionary of English v.0.48:

Flag \Flag\, n. [From Flag to hang loose, to bend down.]
   (Bot.)
   An aquatic plant, with long, ensiform leaves, belonging to
   either of the genera Iris and Acorus.
   [1913 Webster]

   Cooper's flag, the cat-tail (Typha latifolia), the long
      leaves of which are placed between the staves of barrels
      to make the latter water-tight.

   Corn flag. See under 2d Corn.

   Flag broom, a coarse of broom, originally made of flags or
      rushes.

   Flag root, the root of the sweet flag.

   Sweet flag. See Calamus, n., 2.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sweet \Sweet\, a. [Compar. Sweeter; superl. Sweetest.] [OE.
   swete, swote, sote, AS. sw[=e]te; akin to OFries. sw[=e]te,
   OS. sw[=o]ti, D. zoet, G. s["u]ss, OHG. suozi, Icel. saetr,
   soetr, Sw. s["o]t, Dan. s["o]d, Goth. suts, L. suavis, for
   suadvis, Gr. ?, Skr. sv[=a]du sweet, svad, sv[=a]d, to
   sweeten. [root]175. Cf. Assuage, Suave, Suasion.]
   1. Having an agreeable taste or flavor such as that of sugar;
      saccharine; -- opposed to sour and bitter; as, a sweet
      beverage; sweet fruits; sweet oranges.
      [1913 Webster]

   2. Pleasing to the smell; fragrant; redolent; balmy; as, a
      sweet rose; sweet odor; sweet incense.
      [1913 Webster]

            The breath of these flowers is sweet to me.
                                                  --Longfellow.
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   3. Pleasing to the ear; soft; melodious; harmonious; as, the
      sweet notes of a flute or an organ; sweet music; a sweet
      voice; a sweet singer.
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            To make his English sweet upon his tongue.
                                                  --Chaucer.
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            A voice sweet, tremulous, but powerful. --Hawthorne.
      [1913 Webster]

   4. Pleasing to the eye; beautiful; mild and attractive; fair;
      as, a sweet face; a sweet color or complexion.
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            Sweet interchange
            Of hill and valley, rivers, woods, and plains.
                                                  --Milton.
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   5. Fresh; not salt or brackish; as, sweet water. --Bacon.
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   6. Not changed from a sound or wholesome state. Specifically:
      (a) Not sour; as, sweet milk or bread.
      (b) Not state; not putrescent or putrid; not rancid; as,
          sweet butter; sweet meat or fish.
          [1913 Webster]

   7. Plaesing to the mind; mild; gentle; calm; amiable;
      winning; presuasive; as, sweet manners.
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            Canst thou bind the sweet influence of Pleiades?
                                                  --Job xxxviii.
                                                  31.
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            Mildness and sweet reasonableness is the one
            established rule of Christian working. --M. Arnold.
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   Note: Sweet is often used in the formation of self-explaining
         compounds; as, sweet-blossomed, sweet-featured,
         sweet-smelling, sweet-tempered, sweet-toned, etc.
         [1913 Webster]

   Sweet alyssum. (Bot.) See Alyssum.

   Sweet apple. (Bot.)
      (a) Any apple of sweet flavor.
      (b) See Sweet-sop.

   Sweet bay. (Bot.)
      (a) The laurel (Laurus nobilis).
      (b) Swamp sassafras.

   Sweet calabash (Bot.), a plant of the genus Passiflora
      (Passiflora maliformis) growing in the West Indies, and
      producing a roundish, edible fruit, the size of an apple.


   Sweet cicely. (Bot.)
      (a) Either of the North American plants of the
          umbelliferous genus Osmorrhiza having aromatic roots
          and seeds, and white flowers. --Gray.
      (b) A plant of the genus Myrrhis (Myrrhis odorata)
          growing in England.

   Sweet calamus, or Sweet cane. (Bot.) Same as Sweet
      flag, below.

   Sweet Cistus (Bot.), an evergreen shrub (Cistus Ladanum)
      from which the gum ladanum is obtained.

   Sweet clover. (Bot.) See Melilot.

   Sweet coltsfoot (Bot.), a kind of butterbur (Petasites
      sagittata) found in Western North America.

   Sweet corn (Bot.), a variety of the maize of a sweet taste.
      See the Note under Corn.

   Sweet fern (Bot.), a small North American shrub (Comptonia
      asplenifolia syn. Myrica asplenifolia) having
      sweet-scented or aromatic leaves resembling fern leaves.


   Sweet flag (Bot.), an endogenous plant (Acorus Calamus)
      having long flaglike leaves and a rootstock of a pungent
      aromatic taste. It is found in wet places in Europe and
      America. See Calamus, 2.

   Sweet gale (Bot.), a shrub (Myrica Gale) having bitter
      fragrant leaves; -- also called sweet willow, and Dutch
      myrtle. See 5th Gale.

   Sweet grass (Bot.), holy, or Seneca, grass.

   Sweet gum (Bot.), an American tree (Liquidambar
      styraciflua). See Liquidambar.

   Sweet herbs, fragrant herbs cultivated for culinary
      purposes.

   Sweet John (Bot.), a variety of the sweet William.

   Sweet leaf (Bot.), horse sugar. See under Horse.

   Sweet marjoram. (Bot.) See Marjoram.

   Sweet marten (Zool.), the pine marten.

   Sweet maudlin (Bot.), a composite plant (Achillea
      Ageratum) allied to milfoil.

   Sweet oil, olive oil.

   Sweet pea. (Bot.) See under Pea.

   Sweet potato. (Bot.) See under Potato.

   Sweet rush (Bot.), sweet flag.

   Sweet spirits of niter (Med. Chem.) See Spirit of nitrous
      ether, under Spirit.

   Sweet sultan (Bot.), an annual composite plant (Centaurea
      moschata), also, the yellow-flowered (Centaurea
      odorata); -- called also sultan flower.

   Sweet tooth, an especial fondness for sweet things or for
      sweetmeats. [Colloq.]

   Sweet William.
      (a) (Bot.) A species of pink (Dianthus barbatus) of many
          varieties.
      (b) (Zool.) The willow warbler.
      (c) (Zool.) The European goldfinch; -- called also sweet
          Billy. [Prov. Eng.]

   Sweet willow (Bot.), sweet gale.

   Sweet wine. See Dry wine, under Dry.

   To be sweet on, to have a particular fondness for, or
      special interest in, as a young man for a young woman.
      [Colloq.] --Thackeray.
      [1913 Webster]

   Syn: Sugary; saccharine; dulcet; luscious.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Calamus \Cal"a*mus\, n.; pl. Calami. [L., a reed. See Halm.]
   1. (Bot.) The indian cane, a plant of the Palm family. It
      furnishes the common rattan. See Rattan, and Dragon's
      blood.
      [1913 Webster]

   2. (Bot.) A species of Acorus (Acorus calamus), commonly
      called calamus, or sweet flag. The root has a pungent,
      aromatic taste, and is used in medicine as a stomachic;
      the leaves have an aromatic odor, and were formerly used
      instead of rushes to strew on floors.
      [1913 Webster]

   3. (Zool.) The horny basal portion of a feather; the barrel
      or quill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sweet flag
    n 1: perennial marsh plant having swordlike leaves and aromatic
         roots [syn: sweet flag, calamus, sweet calamus,
         myrtle flag, flagroot, Acorus calamus]