1. [n]  something that causes irritation and annoyance; "he's a thorn in my flesh"
2. [n]  a Germanic character of runic origin
3. [n]  a sharp-pointed tip on a stem or leaf

1. \Thorn\, n. [AS. [thorn]orn; akin to OS. & OFries. thorn,
   D. doorn, G. dorn, Dan. torn, Sw. t["o]rne, Icel. [thorn]orn,
   Goth. [thorn]a['u]rnus; cf. Pol. tarn, Russ. tern' the
   blackthorn, ternie thorns, Skr. t[.r][.n]a grass, blade of
   grass. [root]53.]
   1. A hard and sharp-pointed projection from a woody stem;
      usually, a branch so transformed; a spine.
   2. (Bot.) Any shrub or small tree which bears thorns;
      especially, any species of the genus Crat[ae]gus, as the
      hawthorn, whitethorn, cockspur thorn.
   3. Fig.: That which pricks or annoys as a thorn; anything
      troublesome; trouble; care.
            There was given to me a thorn in the flesh, the
            messenger of Satan to buffet me.      --2 Cor. xii.
                                                  7.
            The guilt of empire, all its thorns and cares, Be
            only mine.                            --Southern.
   4. The name of the Anglo-Saxon letter ?, capital form ?. It
      was used to represent both of the sounds of English th, as
      in thin, then. So called because it was the initial letter
      of thorn, a spine.
   {Thorn apple} (Bot.), Jamestown weed.
   {Thorn broom} (Bot.), a shrub that produces thorns.
   {Thorn hedge}, a hedge of thorn-bearing trees or bushes.
   {Thorn devil}. (Zo["o]l.) See {Moloch}, 2.
   {Thorn hopper} (Zo["o]l.), a tree hopper ({Thelia
      crat[ae]gi}) which lives on the thorn bush, apple tree,
      and allied trees.
   

2. \Thorn\, v. t.
   To prick, as with a thorn. [Poetic]
         I am the only rose of all the stock That never thorn'd
         him.                                     --Tennyson.
   

(1.) Heb. hedek (Prov. 15:19), rendered "brier" in Micah 7:4. Some thorny plant, of the Solanum family, suitable for hedges. This is probably the so-called "apple of Sodom," which grows very abundantly in the Jordan valley. "It is a shrubby plant, from 3 to 5 feet high, with very branching stems, thickly clad with spines, like those of the English brier, with leaves very large and woolly on the under side, and thorny on the midriff."

(2.) Heb. kotz (Gen. 3:18; Hos. 10:8), rendered _akantha_ by the LXX. In the New Testament this word _akantha_ is also rendered "thorns" (Matt. 7:16; 13:7; Heb. 6:8). The word seems to denote any thorny or prickly plant (Jer. 12:13). It has been identified with the Ononis spinosa by some.

(3.) Heb. na'atzutz (Isa. 7:19; 55:13). This word has been interpreted as denoting the Zizyphus spina Christi, or the jujube-tree. It is supposed by some that the crown of thorns placed in wanton cruelty by the Roman soldiers on our Saviour's brow before his crucifixion was plaited of branches of this tree. It overruns a great part of the Jordan valley. It is sometimes called the lotus-tree. "The thorns are long and sharp and recurved, and often create a festering wound." It often grows to a great size. (See CROWN OF THORNS.)

(4.) Heb. atad (Ps. 58:9) is rendered in the LXX. and Vulgate by Rhamnus, or Lycium Europoeum, a thorny shrub, which is common all over Palestine. From its resemblance to the box it is frequently called the box-thorn.