Source : Webster's Revised Unabridged Dictionary (1913)

Bur \Bur\, Burr \Burr\, n. [OE. burre burdock; cf. Dan. borre,
   OSw. borra, burdock, thistle; perh. akin to E. bristle (burr-
   for burz-), or perh. to F. bourre hair, wool, stuff; also,
   according to Cotgrave, ``the downe, or hairie coat, wherewith
   divers herbes, fruits, and flowers, are covered,'' fr. L.
   burrae trifles, LL. reburrus rough.]
   1. (Bot.) Any rough or prickly envelope of the seeds of
      plants, whether a pericarp, a persistent calyx, or an
      involucre, as of the chestnut and burdock. Also, any weed
      which bears burs.

            Amongst rude burs and thistles.       --Milton.

            Bur and brake and brier.              --Tennyson.

   2. The thin ridge left by a tool in cutting or shaping metal.
      See {Burr}, n., 2.

   3. A ring of iron on a lance or spear. See {Burr}, n., 4.

   4. The lobe of the ear. See {Burr}, n., 5.

   5. The sweetbread.

   6. A clinker; a partially vitrified brick.

   7. (Mech.)
      (a) A small circular saw.
      (b) A triangular chisel.
      (c) A drill with a serrated head larger than the shank; --
          used by dentists.

   8. [Cf. Gael. borr, borra, a knob, bunch.] (Zo["o]l.) The
      round knob of an antler next to a deer's head. [Commonly
      written {burr}.]

   {Bur oak} (Bot.), a useful and ornamental species of oak
      ({Quercus macrocarpa}) with ovoid acorns inclosed in deep
      cups imbricated with pointed scales. It grows in the
      Middle and Western United States, and its wood is tough,
      close-grained, and durable.

   {Bur reed} (Bot.), a plant of the genus {Sparganium}, having
      long ribbonlike leaves.

Source : WordNet®

Quercus macrocarpa
     n : medium to large deciduous oak of central and eastern North
         America with ovoid acorns deeply immersed in large
         fringed cups; yields tough close-grained wood [syn: {bur
         oak}, {burr oak}, {mossy-cup oak}, {mossycup oak}]