Source : Webster's Revised Unabridged Dictionary (1913)

Yeara \Ye*a"ra\, n. (Bot.)
   The California poison oak ({Rhus diversiloba}). See under
   {Poison}, a.

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.

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

   {Poison ash}. (Bot.)
      (a) A tree of the genus {Amyris} ({A. 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} (Zo["o]l.), 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 ({Rhus
      Toxicodendron}) of North America. It is common on stone
      walls and on the trunks of trees, and has trifoliate,
      rhombic-ovate, variously notched leaves. Many people are
      poisoned by it, if they touch the leaves. See {Poison
      sumac}. Called also {poison oak}, and {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.), the poison ivy; also, the more shrubby
      {Rhus diversiloba} of California and Oregon.

   {Poison sac}. (Zo["o]l.) Same as {Poison gland}, above. See
      Illust. under {Fang}.

   {Poison sumac} (Bot.), a poisonous shrub of the genus {Rhus}
      ({R. venenata}); -- 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 ({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.

   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.

Source : WordNet®

Rhus diversiloba
     n : poisonous shrub of the Pacific coast of North America that
         causes a rash on contact [syn: {western poison oak}, {Toxicodendron
         diversilobum}]