Source : Webster's Revised Unabridged Dictionary (1913)

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.

Hemlock \Hem"lock\, n. [OE. hemeluc, humloc, AS. hemlic,
   hymlic.]
   1. (Bot.) The name of several poisonous umbelliferous herbs
      having finely cut leaves and small white flowers, as the
      {Cicuta maculata}, {bulbifera}, and {virosa}, and the
      {Conium maculatum}. See {Conium}.

   Note: The potion of hemlock administered to Socrates is by
         some thought to have been a decoction of {Cicuta
         virosa}, or water hemlock, by others, of {Conium
         maculatum}.

   2. (Bot.) An evergreen tree common in North America ({Abies,
      or Tsuga, Canadensis}); hemlock spruce.

            The murmuring pines and the hemlocks. --Longfellow.

   3. The wood or timber of the hemlock tree.

   {Ground hemlock}, or {Dwarf hemlock}. See under {Ground}.

Hemlock \Hem"lock\, n. [OE. hemeluc, humloc, AS. hemlic,
   hymlic.]
   1. (Bot.) The name of several poisonous umbelliferous herbs
      having finely cut leaves and small white flowers, as the
      {Cicuta maculata}, {bulbifera}, and {virosa}, and the
      {Conium maculatum}. See {Conium}.

   Note: The potion of hemlock administered to Socrates is by
         some thought to have been a decoction of {Cicuta
         virosa}, or water hemlock, by others, of {Conium
         maculatum}.

   2. (Bot.) An evergreen tree common in North America ({Abies,
      or Tsuga, Canadensis}); hemlock spruce.

            The murmuring pines and the hemlocks. --Longfellow.

   3. The wood or timber of the hemlock tree.

   {Ground hemlock}, or {Dwarf hemlock}. See under {Ground}.

Conine \Co"nine\ (? or ?), n. [From {Conium}.] (Chem.)
   A powerful and very poisonous vegetable alkaloid found in the
   hemlock ({Conium maculatum}) and extracted as a colorless
   oil, {C8H17N}, of strong repulsive odor and acrid taste. It
   is regarded as a derivative of piperidine and likewise of one
   of the collidines. It occasions a gradual paralysis of the
   motor nerves. Called also {coniine}, {coneine}, {conia}, etc.
   See {Conium}, 2.

Conhydrine \Con*hy"drine\ (? or ?), n. [Conium + hydrate.]
   (Chem.)
   A vegetable alkaloid found with conine in the poison hemlock
   ({Conium maculatum}). It is a white crystalline substance,
   {C8H17NO}, easily convertible into conine.



   2. (Med.) The common hemlock ({Conium maculatum}, poison
      hemlock, spotted hemlock, poison parsley), a roadside weed
      of Europe, Asia, and America, cultivated in the United
      States for medicinal purpose. It is an active poison. The
      leaves and fruit are used in medicine.

Source : WordNet®

Conium maculatum
     n : large branching biennial herb native to Eurasia and Africa
         and adventive in North America having large fernlike
         leaves and white flowers; usually found in damp habitats;
         all parts extremely poisonous [syn: {hemlock}, {poison
         hemlock}, {poison parsley}, {California fern}, {Nebraska
         fern}, {winter fern}]