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

After more than a decade of monitoring, the report showed concentrations of phosphorus are on track to deplete the harbor's ecosystem in years to come, according to our media partner, The Baltimore Banner. —Adam Thompson, CBS News, 8 May 2026

These soybeans also provide a variety of nutrients—including B vitamins, calcium, copper, magnesium, phosphorus, potassium, and iron—that support metabolic, immune, bone, and heart health. —Christina Manian, Health, 6 May 2026

While both oatmeal and millet are rich in manganese, phosphorus, and magnesium, millet provides antioxidants that can help reduce oxidative stress. —Mira Miller, Verywell Health, 4 May 2026

The numbers indicate the ratio (by percentage) of nitrogen, phosphorus, and potassium (NPK), in that order, in the fertilizer. —David Beaulieu, The Spruce, 1 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