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

By cooling an atomically thin crystal of nickel phosphorus trisulfide, or NiPS3, the team observed a full sequence of exotic magnetic phases predicted in the 1970s but never fully demonstrated in a single system. —Neetika Walter, Interesting Engineering, 3 Mar. 2026

The Bay Restoration Fund, created in 2004, is used to finance upgrades to wastewater treatment plants and septic system improvements aimed at reducing nitrogen and phosphorus pollution to the Chesapeake Bay. —Josh Davis, Baltimore Sun, 2 Mar. 2026

When plants reach 3 inches tall, add a slow-release fertilizer high in phosphorus. —Barbara Gillette, The Spruce, 27 Feb. 2026

Understanding soil pH and nutrient availability Once results are received, a basic soil test will reveal the pH level and amounts of phosphorus and potassium present in your soil. —Anthony Reardon, Kansas City Star, 25 Feb. 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