Source : Webster's Revised Unabridged Dictionary (1913)

Scrub \Scrub\, n.
   1. One who labors hard and lives meanly; a mean fellow. ``A
      sorry scrub.'' --Bunyan.

            We should go there in as proper a manner possible;
            nor altogether like the scrubs about us.
                                                  --Goldsmith.

   2. Something small and mean.

   3. A worn-out brush. --Ainsworth.

   4. A thicket or jungle, often specified by the name of the
      prevailing plant; as, oak scrub, palmetto scrub, etc.

   5. (Stock Breeding) One of the common live stock of a region
      of no particular breed or not of pure breed, esp. when
      inferior in size, etc. [U.S.]

   {Scrub bird} (Zo["o]l.), an Australian passerine bird of the
      family {Atrichornithid[ae]}, as {Atrichia clamosa}; --
      called also {brush bird}.

   {Scrub oak} (Bot.), the popular name of several dwarfish
      species of oak. The scrub oak of New England and the
      Middle States is {Quercus ilicifolia}, a scraggy shrub;
      that of the Southern States is a small tree ({Q.
      Catesb[ae]i}); that of the Rocky Mountain region is {Q.
      undulata}, var. Gambelii.

   {Scrub robin} (Zo["o]l.), an Australian singing bird of the
      genus {Drymodes}.

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®

scrub oak
     n : any of various chiefly American small shrubby oaks often a
         dominant form on thin dry soils sometimes forming dense
         thickets