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

The far side is thought to have fewer heat-producing elements, such as uranium, thorium, potassium, phosphorus and rare earth elements — collectively referred to as KREEP. —Samantha Mathewson, Space.com, 30 Sep. 2025

Use high-nitrogen, low-phosphorus blends to protect waterways and follow local rules. —Charlotte Germane, Better Homes & Gardens, 26 Sep. 2025

Whole seeds provide more fiber, potassium, and zinc, while shelled pepitas offer more protein, fat, iron, magnesium, and phosphorus. —Johna Burdeos, Health, 19 Sep. 2025

Some researchers have recently developed flame-retardant, hydrophobic, high-strength, breathable cotton fabric by dual covalent crosslinking of amino-containing siloxane segments, phosphorus-containing monomers with several reaction sites, and hydroxyl-rich cellulose segments. —Prabhat Ranjan Mishra, Interesting Engineering, 18 Sep. 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