Source : Webster's Revised Unabridged Dictionary (1913)

Sow \Sow\, n. [OE. sowe, suwe, AS. sugu, akin to s[=u], D. zog,
   zeug, OHG. s[=u], G. sau, Icel. s[=y]r, Dan. so, Sw. sugga,
   so, L. sus. Gr. "y^s, sy^s, Zend. hu boar; probably from the
   root seen in Skr. s[=u] to beget, to bear; the animal being
   named in allusion to its fecundity. [root]294. Cf. {Hyena},
   {Soil} to stain, {Son}, {Swine}.]
   1. (Zo["o]l.) The female of swine, or of the hog kind.

   2. (Zo["o]l.) A sow bug.

   3. (Metal.)
      (a) A channel or runner which receives the rows of molds
          in the pig bed.
      (b) The bar of metal which remains in such a runner.
      (c) A mass of solidified metal in a furnace hearth; a
          salamander.

   4. (Mil.) A kind of covered shed, formerly used by besiegers
      in filling up and passing the ditch of a besieged place,
      sapping and mining the wall, or the like. --Craig.

   {Sow bread}. (Bot.) See {Cyclamen}.

   {Sow bug}, or {Sowbug} (Zo["o]l.), any one of numerous
      species of terrestrial Isopoda belonging to {Oniscus},
      {Porcellio}, and allied genera of the family
      {Oniscid[ae]}. They feed chiefly on decaying vegetable
      substances.

   {Sow thistle} [AS. sugepistel] (Bot.), a composite plant
      ({Sonchus oleraceus}) said to be eaten by swine and some
      other animals.

Thistle \This"tle\, n. [OE. thistil, AS. [thorn]istel; akin to
   D. & G. distel, OHG. distila, distil, Icel. [thorn]istill,
   Sw. tistel, Dan. tidsel; of uncertain origin.] (Bot.)
   Any one of several prickly composite plants, especially those
   of the genera {Cnicus}, {Craduus}, and {Onopordon}. The name
   is often also applied to other prickly plants.

   {Blessed thistle}, {Carduus benedictus}, so named because it
      was formerly considered an antidote to the bite of
      venomous creatures.

   {Bull thistle}, {Cnicus lanceolatus}, the common large
      thistle of neglected pastures.

   {Canada thistle}, {Cnicus arvensis}, a native of Europe, but
      introduced into the United States from Canada.

   {Cotton thistle}, {Onopordon Acanthium}.

   {Fuller's thistle}, the teasel.

   {Globe thistle}, {Melon thistle}, etc. See under {Globe},
      {Melon}, etc.

   {Pine thistle}, {Atractylis gummifera}, a native of the
      Mediterranean region. A vicid gum resin flows from the
      involucre.

   {Scotch thistle}, either the cotton thistle, or the musk
      thistle, or the spear thistle; -- all used national
      emblems of Scotland.

   {Sow thistle}, {Sonchus oleraceus}.

   {Spear thistle}. Same as {Bull thistle}.

   {Star thistle}, a species of {Centaurea}. See {Centaurea}.

   {Torch thistle}, a candelabra-shaped plant of the genus
      Cereus. See {Cereus}.

   {Yellow thistle}, {Cincus horridulus}.

   {Thistle bird} (Zo["o]l.), the American goldfinch, or
      yellow-bird ({Spinus tristis}); -- so called on account of
      its feeding on the seeds of thistles. See Illust. under
      {Goldfinch}.

   {Thistle butterfly} (Zo["o]l.), a handsomely colored American
      butterfly ({Vanessa cardui}) whose larva feeds upon
      thistles; -- called also {painted lady}.

   {Thistle cock} (Zo["o]l.), the corn bunting ({Emberiza
      militaria}). [Prov. Eng.]

   {Thistle crown}, a gold coin of England of the reign of James
      I., worth four shillings.

   {Thistle finch} (Zo["o]l.), the goldfinch; -- so called from
      its fondness for thistle seeds. [Prov. Eng.]

   {Thistle funnel}, a funnel having a bulging body and flaring
      mouth.

Source : WordNet®

sow thistle
     n : any of several Old World coarse prickly-leaved shrubs and
         subshrubs having milky juice and yellow flowers; widely
         naturalized; often noxious weeds in cultivated soil [syn:
          {milk thistle}]