The Collaborative International Dictionary of English v.0.48:

Phosphorus \Phos"phor*us\ (f[o^]s"f[o^]r*[u^]s), n.; pl.
   Phosphori (f[o^]s"f[o^]r*[imac]). [L., the morning star,
   Gr. fwsfo`ros, lit., light bringer; fw^s light + fe`rein to
   bring.]
   1. The morning star; Phosphor.
      [1913 Webster]

   2. (Chem.) A poisonous nonmetallic element of the nitrogen
      group, obtained as a white, or yellowish, translucent waxy
      substance, having a characteristic disagreeable smell;
      this waxy allotropic form is also called yellow
      phosphorus, to distinguish it from another allotropic
      form, red phosphorus. It is very active chemically, must
      be preserved under water, and unites with oxygen even at
      ordinary temperatures, giving a faint glow, -- whence its
      name. It always occurs combined, usually in phosphates, as
      in the mineral apatite, in bones, etc. It is used in the
      composition on the tips of friction matches, and for many
      other purposes. It is an essential component of the
      genetic material of all living organisms. The molecule
      contains four atoms. Symbol P. Atomic weight 31.0.
      [1913 Webster]

   3. (Chem.) Hence, any substance which shines in the dark like
      phosphorus, as certain phosphorescent bodies.
      [1913 Webster]

   Bologna phosphorus (Chem.), sulphide of barium, which
      shines in the dark after exposure to light; -- so called
      because this property was discovered by a resident of
      Bologna. The term is sometimes applied to other compounds
      having similar properties.

   Metallic phosphorus (Chem.), an allotropic modification of
      phosphorus, obtained as a gray metallic crystalline
      substance, having very inert chemical properties. It is
      obtained by heating ordinary phosphorus in a closed vessel
      at a high temperature.

   Phosphorus disease (Med.), a disease common among workers
      in phosphorus, giving rise to necrosis of the jawbone, and
      other symptoms.

   Red phosphorus, or Amorphous phosphorus (Chem.), an
      allotropic modification of phosphorus, obtained as a dark
      red powder by heating ordinary phosphorus in closed
      vessels. It is not poisonous, is not phosphorescent, and
      is only moderately active chemically. It is valuable as a
      chemical reagent, and is used in the composition of the
      friction surface on which safety matches are ignited.

   Solar phosphori (Chem.), phosphorescent substances which
      shine in the dark after exposure to the sunlight or other
      intense light.

   yellow phosphorus (Chem.), the waxy yellow allotropic form
      of elemental phosphorus. See also phosphorus[2].
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

phosphorus
    n 1: a multivalent nonmetallic element of the nitrogen family
         that occurs commonly in inorganic phosphate rocks and as
         organic phosphates in all living cells; is highly reactive
         and occurs in several allotropic forms [syn: phosphorus,
         P, atomic number 15]
    2: a planet (usually Venus) seen just before sunrise in the
       eastern sky [syn: morning star, daystar, Phosphorus,
       Lucifer]

The Elements (07Nov00):

phosphorus
Symbol: P
Atomic number: 15
Atomic weight: 30.9738
Non-metallic element belonging to group 15 of the periodic table. Has a
multiple allotropic forms. Essential element for living organisms. It
was
discovered by Brandt in 1669.