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phos·pho·rus (fŏsfər-əs)
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n.
1. Symbol P A highly reactive, poisonous, nonmetallic element occurring naturally in phosphates, especially apatite, and existing in three allotropic forms, white (or sometimes yellow), red, and black (or violet). An essential element for biological cells, it is used in safety matches, pyrotechnics, incendiary shells, and fertilizers and to protect metal surfaces from corrosion. Atomic number 15; atomic weight 30.9738; melting point (white) 44.15°C; boiling point 280.5°C; specific gravity (white) 1.82, (red) 2.16, (black) 2.25 to 2.69; valence 3, 4, 5. See Periodic Table.
2. A phosphorescent substance.
3. Phosphorus Astronomy See Lucifer.

[Modern Latin phōsphorus, substance or organism that emits light, phosphorus, Latin Phōsphorus, morning star, from Greek phōsphoros, bringing light, morning star : phōs, light; see bhā-1 in the Appendix of Indo-European roots + -phoros, -phorous.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.