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

Test the soil before adding phosphorus, since high phosphorus can reduce the plant’s reliance on mycorrhizae. — Dr. Avishesh Neupane, Hartford Courant, 9 Aug. 2026

For years, Florida environmental groups accused the family’s operations south of Lake Okeechobee of contributing phosphorus pollution to the Everglades, while critics questioned labor conditions on Dominican Republic plantations. — Miami Herald, 7 Aug. 2026

Using a water-soluble fertilizer with an NPK ratio of 15-30-15 will give the plants a boost of the phosphorus needed to help your flowers start producing buds and blossoms again. — Mary Marlowe Leverette, Southern Living, 6 Aug. 2026

On July 28, the Pyeongtaek city government sent text messages advising its residents to move to safe places and avoid skin exposure, saying white phosphorus was leaked at the Osan Air Base in the city, which is just south of Seoul, the capital. — ABC News, 6 Aug. 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