phosphorus

noun

phos·​pho·​rus ˈfäs-f(ə-)rəs 

often attributive

1

: a phosphorescent substance or body

especially : one that shines or glows in the dark

2

or less commonly phosphorous

ˈfäs-f(ə-)rəs 

: a nonmetallic element of the nitrogen family with atomic number 15 that occurs widely in combination especially as phosphates, that is essential for life in all known organisms, and that is used especially in fertilizers and organophosphorus compounds see Chemical Elements Table

Examples of phosphorus in a Sentence

Recent Examples on the Web

To get your cucumber plant to produce more flowers, apply a phosphorus-rich fertilizer. —Shelby Vittek, The Spruce, 13 May 2026

Best Fertilizers for Fruit Trees Fertilizers with an NPK (nitrogen, phosphorus, and potassium) ratio of 10-10-10 are widely used to fertilize fruit trees, as these nutrients are essential for healthy growth, developing a strong root system, and producing fruit. —Sj McShane, Martha Stewart, 13 May 2026

That influx of nutrients, including nitrogen and phosphorus, creates ideal conditions for invasive species when water slows in wetlands like this one. —ABC News, 12 May 2026

In addition to vitamin C, guava is also a good source of vitamin A, iron, calcium, phosphorus, and minerals. —Sarah Bence, Verywell Health, 12 May 2026

Word History

Etymology

New Latin, from Greek phōsphoros light-bearing — more at phosphor

First Known Use

1680, in the meaning defined at sense 1

Rhymes for phosphorus

• phosphorous
• organophosphorus

Kids Definition

phosphorus

noun

phos·​pho·​rus ˈfäs-f(ə-)rəs 

1

: a phosphorescent substance

especially : one that glows in the dark

2

: a nonmetallic element that occurs widely especially as phosphates see element

phosphoric

fäs-ˈfȯr-ik, 

-ˈfär-

adjective

phosphorous

ˈfäs-f(ə-)rəs;

fäs-ˈfōr-əs, 

-ˈfȯr-

adjective

Medical Definition

phosphorus

noun

phos·​pho·​rus ˈfäs-f(ə-)rəs 

often attributive

: a nonmetallic multivalent element that occurs widely in combined form especially as inorganic phosphates in minerals, soils, natural waters, bones, and teeth and as organic phosphates in all living cells and that exists in several allotropic forms

—symbol P see Chemical Elements Table