Source : Webster's Revised Unabridged Dictionary (1913)

Oak \Oak\ ([=o]k), n. [OE. oke, ok, ak, AS. [=a]c; akin to D.
   eik, G. eiche, OHG. eih, Icel. eik, Sw. ek, Dan. eeg.]
   1. (Bot.) Any tree or shrub of the genus {Quercus}. The oaks
      have alternate leaves, often variously lobed, and
      staminate flowers in catkins. The fruit is a smooth nut,
      called an {acorn}, which is more or less inclosed in a
      scaly involucre called the cup or cupule. There are now
      recognized about three hundred species, of which nearly
      fifty occur in the United States, the rest in Europe,
      Asia, and the other parts of North America, a very few
      barely reaching the northern parts of South America and
      Africa. Many of the oaks form forest trees of grand
      proportions and live many centuries. The wood is usually
      hard and tough, and provided with conspicuous medullary
      rays, forming the silver grain.

   2. The strong wood or timber of the oak.

   Note: Among the true oaks in America are:

   {Barren oak}, or

   {Black-jack}, {Q. nigra}.

   {Basket oak}, {Q. Michauxii}.

   {Black oak}, {Q. tinctoria}; -- called also {yellow} or
      {quercitron oak}.

   {Bur oak} (see under {Bur}.), {Q. macrocarpa}; -- called also
      {over-cup} or {mossy-cup oak}.

   {Chestnut oak}, {Q. Prinus} and {Q. densiflora}.

   {Chinquapin oak} (see under {Chinquapin}), {Q. prinoides}.

   {Coast live oak}, {Q. agrifolia}, of California; -- also
      called {enceno}.

   {Live oak} (see under {Live}), {Q. virens}, the best of all
      for shipbuilding; also, {Q. Chrysolepis}, of California.
      

   {Pin oak}. Same as {Swamp oak}.

   {Post oak}, {Q. obtusifolia}.

   {Red oak}, {Q. rubra}.

   {Scarlet oak}, {Q. coccinea}.

   {Scrub oak}, {Q. ilicifolia}, {Q. undulata}, etc.

   {Shingle oak}, {Q. imbricaria}.

   {Spanish oak}, {Q. falcata}.

   {Swamp Spanish oak}, or

   {Pin oak}, {Q. palustris}.

   {Swamp white oak}, {Q. bicolor}.

   {Water oak}, {Q. aguatica}.

   {Water white oak}, {Q. lyrata}.

   {Willow oak}, {Q. Phellos}. Among the true oaks in Europe
      are:

   {Bitter oak}, or

   {Turkey oak}, {Q. Cerris} (see {Cerris}).

   {Cork oak}, {Q. Suber}.

   {English white oak}, {Q. Robur}.

   {Evergreen oak},

   {Holly oak}, or

   {Holm oak}, {Q. Ilex}.

   {Kermes oak}, {Q. coccifera}.

   {Nutgall oak}, {Q. infectoria}.

   Note: Among plants called oak, but not of the genus
         {Quercus}, are:

   {African oak}, a valuable timber tree ({Oldfieldia
      Africana}).

   {Australian, or She}, {oak}, any tree of the genus
      {Casuarina} (see {Casuarina}).

   {Indian oak}, the teak tree (see {Teak}).

   {Jerusalem oak}. See under {Jerusalem}.

   {New Zealand oak}, a sapindaceous tree ({Alectryon
      excelsum}).

   {Poison oak}, the poison ivy. See under {Poison}.

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®

bur oak
     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: {burr
         oak}, {mossy-cup oak}, {mossycup oak}, {Quercus
         macrocarpa}]