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}.

Source : WordNet®

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