Source : Webster's Revised Unabridged Dictionary (1913)

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.

Blessed thistle \Bless"ed this"tle\
   See under {Thistle}.

Source : WordNet®

blessed thistle
     n 1: tall Old World biennial thistle with large clasping
          white-blotched leaves and purple flower heads;
          naturalized in California and South America [syn: {milk
          thistle}, {lady's thistle}, {Our Lady's mild thistle}, {holy
          thistle}, {Silybum marianum}]
     2: annual of Mediterranean to Portugal having hairy stems and
        minutely spiny-toothed leaves and large heads of yellow
        flowers [syn: {sweet sultan}, {Cnicus benedictus}]