The Collaborative International Dictionary of English v.0.48:

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.]
   [1913 Webster]
   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.
      [1913 Webster]

   2. The strong wood or timber of the oak.
      [1913 Webster]

   Note: Among the true oaks in America are:

   Barren oak, or

   Black-jack, Quercus nigra.

   Basket oak, Quercus Michauxii.

   Black oak, Quercus tinctoria; -- called also yellow oak
      or quercitron oak.

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

   Chestnut oak, Quercus Prinus and Quercus densiflora.

   Chinquapin oak (see under Chinquapin), Quercus
      prinoides.

   Coast live oak, Quercus agrifolia, of California; -- also
      called enceno.

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

   Pin oak. Same as Swamp oak.

   Post oak, Quercus obtusifolia.

   Red oak, Quercus rubra.

   Scarlet oak, Quercus coccinea.

   Scrub oak, Quercus ilicifolia, Quercus undulata, etc.


   Shingle oak, Quercus imbricaria.

   Spanish oak, Quercus falcata.

   Swamp Spanish oak, or

   Pin oak, Quercus palustris.

   Swamp white oak, Quercus bicolor.

   Water oak, Quercus aquatica.

   Water white oak, Quercus lyrata.

   Willow oak, Quercus Phellos.
      [1913 Webster] Among the true oaks in Europe are:

   Bitter oak, or

   Turkey oak, Quercus Cerris (see Cerris).

   Cork oak, Quercus Suber.

   English white oak, Quercus Robur.

   Evergreen oak,

   Holly oak, or

   Holm oak, Quercus Ilex.

   Kermes oak, Quercus coccifera.

   Nutgall oak, Quercus infectoria.
      [1913 Webster]

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

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

   Australian oak 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, a shrub once not distinguished from poison ivy,
      but now restricted to Rhus toxicodendron or Rhus
      diversiloba.

   Silky oak or Silk-bark oak, an Australian tree
      (Grevillea robusta).
      [1913 Webster]

   Green oak, oak wood colored green by the growth of the
      mycelium of certain fungi.

   Oak apple, a large, smooth, round gall produced on the
      leaves of the American red oak by a gallfly (Cynips
      confluens). It is green and pulpy when young.

   Oak beauty (Zool.), a British geometrid moth (Biston
      prodromaria) whose larva feeds on the oak.

   Oak gall, a gall found on the oak. See 2d Gall.

   Oak leather (Bot.), the mycelium of a fungus which forms
      leatherlike patches in the fissures of oak wood.

   Oak pruner. (Zool.) See Pruner, the insect.

   Oak spangle, a kind of gall produced on the oak by the
      insect Diplolepis lenticularis.

   Oak wart, a wartlike gall on the twigs of an oak.

   The Oaks, one of the three great annual English horse races
      (the Derby and St. Leger being the others). It was
      instituted in 1779 by the Earl of Derby, and so called
      from his estate.

   To sport one's oak, to be "not at home to visitors,"
      signified by closing the outer (oaken) door of one's
      rooms. [Cant, Eng. Univ.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Poison \Poi"son\, n. [F. poison, in Old French also, a potion,
   fr. L. potio a drink, draught, potion, a poisonous draught,
   fr. potare to drink. See Potable, and cf. Potion.]
   1. Any agent which, when introduced into the animal organism,
      is capable of producing a morbid, noxious, or deadly
      effect upon it; as, morphine is a deadly poison; the
      poison of pestilential diseases.
      [1913 Webster]

   2. That which taints or destroys moral purity or health; as,
      the poison of evil example; the poison of sin.
      [1913 Webster]

   Poison ash. (Bot.)
      (a) A tree of the genus Amyris (Amyris balsamifera)
          found in the West Indies, from the trunk of which a
          black liquor distills, supposed to have poisonous
          qualities.
      (b) The poison sumac (Rhus venenata). [U. S.]

   Poison dogwood (Bot.), poison sumac.

   Poison fang (Zool.), one of the superior maxillary teeth of
      some species of serpents, which, besides having the cavity
      for the pulp, is either perforated or grooved by a
      longitudinal canal, at the lower end of which the duct of
      the poison gland terminates. See Illust. under Fang.

   Poison gland (Biol.), a gland, in animals or plants, which
      secretes an acrid or venomous matter, that is conveyed
      along an organ capable of inflicting a wound.

   Poison hemlock (Bot.), a poisonous umbelliferous plant
      (Conium maculatum). See Hemlock.

   Poison ivy (Bot.), a poisonous climbing plant (formerly
      Rhus Toxicodendron, or Rhus radicans, now classified
      as Toxicodendron radicans) of North America. It is
      common as a climbing vine, especially found on tree
      trunks, or walls, or as a low, spreading vine or as a
      shrub. As a low vine it grows well in lightly shaded
      areas, recognizable by growing in clusters of three
      leaves. Its leaves are trifoliate, rhombic-ovate, and
      variously notched. Its form varies slightly from location
      to location, leading to some speculation that it may
      consist of more than one species. Many people are poisoned
      by it, though some appear resistant to its effects.
      Touching the leaves may leave a residue of an oil on the
      skin, and if not washed off quickly, sensitive areas of
      skin become reddened and develop multiple small blisters,
      lasting for several days to several weeks, and causing a
      persistent itch. The toxic reaction is due to an oil,
      present in all parts of the plant except the pollen,
      called urushiol, the active component of which is the
      compound pentadecylacatechol (according to [a

      href="http:]/www.jaxmed.com/articles/Diseases/poison_ivy_dermatitis.htm">Charles
      H. Booras). See Poison sumac. It is related to poison
      oak, and is also called mercury.

   Poison nut. (Bot.)
      (a) Nux vomica.
      (b) The tree which yields this seed (Strychnos
          Nuxvomica). It is found on the Malabar and Coromandel
          coasts.

   Poison oak (Bot.), a dermatitis-producing plant often
      lumped together with the poison ivy (Toxicodendron
      radicans) in common terminology, but more properly
      distinguished as the more shrubby Toxicodendron
      quercifolium (syn. Toxicodendron diversilobum), common
      in California and Oregon. Opinion varies as to whether the
      poison oak and poison ivy are only variants of a single
      species. See poison ivy, above.

   Poison sac. (Zool.) Same as Poison gland, above. See
      Illust. under Fang.

   Poison sumac (Bot.), a poisonous shrub formerly considered
      to be of the genus Rhus (Rhus venenata), but now
      classified as Toxicodendron vernix; -- also called
      poison ash, poison dogwood, and poison elder. It has
      pinnate leaves on graceful and slender common petioles,
      and usually grows in swampy places. Both this plant and
      the poison ivy (Toxicodendron radicans, formerly Rhus
      Toxicodendron) have clusters of smooth greenish white
      berries, while the red-fruited species of this genus are
      harmless. The tree (Rhus vernicifera) which yields the
      celebrated Japan lacquer is almost identical with the
      poison sumac, and is also very poisonous. The juice of the
      poison sumac also forms a lacquer similar to that of
      Japan.
      [1913 Webster +PJC]

   Syn: Venom; virus; bane; pest; malignity.

   Usage: Poison, Venom. Poison usually denotes something
          received into the system by the mouth, breath, etc.
          Venom is something discharged from animals and
          received by means of a wound, as by the bite or sting
          of serpents, scorpions, etc. Hence, venom specifically
          implies some malignity of nature or purpose.
          [1913 Webster]

WordNet (r) 3.0 (2006):

poison oak
    n 1: dermatitis resulting from contact with a poison oak plant
    2: climbing plant common in eastern and central United States
       with ternate leaves and greenish flowers followed by white
       berries; yields an irritating oil that causes a rash on
       contact [syn: poison ivy, markweed, poison mercury,
       poison oak, Toxicodendron radicans, Rhus radicans]