Jump To:

• phosphorus
  phosphorus

  noun

  a solid, nonmetallic element existing in at least three allotropic forms, one that is yellow, poisonous, flammable, and luminous in the dark, one that is red, less poisonous, and less flammable, and another that is black, insoluble in most solvents, and the least flammable. The element is used in forming smoke screens, its compounds are used in matches and phosphate fertilizers, and it is a necessary constituent of plant and animal life in bones, nerves, and embryos. P; 30.974; 15; (yellow) 1.82 at 20°C, (red) 2.20 at 20°C, (black) 2.25–2.69 at 20°C.
• Phosphorus
  Phosphorus

  noun

  Phosphor.

phosphorus

¹ American  

[fos-fer-uhs] / ˈfɒs fər əs /

noun

phosphori plural

1. Chemistry. a solid, nonmetallic element existing in at least three allotropic forms, one that is yellow, poisonous, flammable, and luminous in the dark, one that is red, less poisonous, and less flammable, and another that is black, insoluble in most solvents, and the least flammable. The element is used in forming smoke screens, its compounds are used in matches and phosphate fertilizers, and it is a necessary constituent of plant and animal life in bones, nerves, and embryos. P; 30.974; 15; (yellow) 1.82 at 20°C, (red) 2.20 at 20°C, (black) 2.25–2.69 at 20°C.

2. any phosphorescent substance.

3. phosphor.

---

Phosphorus ² American  

[fos-fer-uhs] / ˈfɒs fər əs /

noun

1. Phosphor.

---

Phosphorus ¹ British  

/ ˈfɒsfərəs /

noun

1. a morning star, esp Venus

---

phosphorus ² British  

/ ˈfɒsfərəs /

noun

1. an allotropic nonmetallic element occurring in phosphates and living matter. Ordinary phosphorus is a toxic flammable phosphorescent white solid; the red form is less reactive and nontoxic: used in matches, pesticides, and alloys. The radioisotope phosphorus-32 ( radiophosphorus ), with a half-life of 14.3 days, is used in radiotherapy and as a tracer. Symbol: P; atomic no: 15; atomic wt: 30.973 762; valency: 3 or 5; relative density: 1.82 (white), 2.20 (red); melting pt: 44.1°C (white); boiling pt: 280°C (white)

2. a less common name for a phosphor

---

phosphorus Scientific  

/ fŏs′fər-əs /

1. A highly reactive, poisonous nonmetallic element occurring naturally in phosphates, especially in the mineral apatite. It exists in white (or sometimes yellow), red, and black forms, and is an essential component of protoplasm. Phosphorus is used to make matches, fireworks, and fertilizers and to protect metal surfaces from corrosion. Atomic number 15; atomic weight 30.9738; melting point (white) 44.1°C; boiling point 280°C; specific gravity (white) 1.82; valence 3, 5.

2. See Periodic Table

---

Other Word Forms

Noun Inflected Forms

• phosphori
  plural

Etymology

Origin of phosphorus

1620–30; < New Latin phōsphorus phosphorus; Latin: morning star; see Phosphor

Example Sentences

The answer, for that sample, was: mostly Desmodesmus, a green algae that gobbles up phosphorus and nitrogen.

From Slate • Jun. 27, 2026

Untreated sewage is high in nitrogen and phosphorus.

From Los Angeles Times • Jun. 20, 2026

The results deliver readings for specific nutrients such as nitrogen, phosphorus and potassium so that each field can get the right fertilizer, with the right amount of nutrients it needs for more efficient production.

From MarketWatch • Jun. 2, 2026

“The nitrogen cycle, phosphorus cycle, carbon cycle—these fundamental reactions are happening across the globe, but in a wastewater plant it’s happening on steroids,” he said.

From The Wall Street Journal • May 14, 2026

It was largely because of this mastery of phosphorus that Sweden became, and remains, a leading producer of matches.

From "A Short History of Nearly Everything" by Bill Bryson