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

For coffee grounds to release their nitrogen, phosphorus, and potassium, they must first be processed by soil microbes. — Leanne Potts, Better Homes & Gardens, 19 Sep. 2026

These areas have collectively met 100% of their goal for sediment reduction, 90% of their goal for phosphorus reduction, and 57% of their goal for nitrogen reduction, according to Wednesday's statement. — Bryan Lynn, CBS News, 17 Sep. 2026

And kefir contains potassium and phosphorus, Halperin notes, which are important for fluid balance, muscle and nerve function and bone health. — Daryl Austin, USA Today, 16 Sep. 2026

The strategy has relied on voluntary action, asking farmers to adopt conservation practices such as planting cover crops to slow runoff and reduce nitrogen and phosphorus pollution flowing into waterways. — Nick El Hajj, Des Moines Register, 15 Sep. 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