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

Pets, on the other hand, have commercial diets that introduce nitrogen and phosphorus to the environment, according to Leave No Trace, a nonprofit that aims to protect the outdoors. —Gina Lee Castro, jsonline.com, 11 Aug. 2025

But in samples from California’s Mono Lake, a research team had found evidence of a bacterium swapping out phosphorus for arsenic. —Dan Vergano, Scientific American, 24 July 2025

There’s silver dust in the cells, and some boron and phosphorus, critical additives to increase conductivity and to provide the necessary environment for photons from sunlight to knock electrons loose from the silicon. —Bill McKibben, New Yorker, 9 July 2025

That report cited a number of reasons for the struggle to attain the 2025 goals — and for the bay’s lackluster response to the pollution reductions achieved thus far — including the possibility that the Bay Program’s current computer model could be overestimating phosphorus reductions. —Christine Condon, Baltimore Sun, 8 July 2025

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