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

According to the United States Environmental Protection Agency, excess nitrogen and phosphorus in waterways cause algae blooms that decrease oxygen available for other aquatic life. —Kate Gray, CBS News, 12 June 2026

Products with slightly higher phosphorus levels, indicated by the middle number in the fertilizer ratio, such as 5-10-5 or 10-30-20, are ideal. —Rachel Silva, Martha Stewart, 11 June 2026

Excess nutrients, particularly phosphorus carried into the lake through stormwater runoff, can lead to algae blooms that absorb sunlight and warm the water. —Tyler Quattrin, Twin Cities, 10 June 2026

Start with nitrogen-rich fertilizer at transplanting, then switch to phosphorus-rich for better yields. —Mallory Carra, The Spruce, 9 June 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