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

Tea is a green compost containing about 4 percent nitrogen and a small amount of potassium and phosphorus. —Brandee Gruener, Southern Living, 28 Apr. 2025

However, if the soil pH or phosphorus levels are low, ground limestone and bonemeal can be mixed into the backfill. —Dawn Pettinelli, Hartford Courant, 26 Apr. 2025

Indeed, just two small plums (100 grams), contain protein, calcium, magnesium, phosphorus, potassium, zinc, biotin, vitamin K, vitamin C and more than a gram of dietary fiber, per the U.S. Department of Agriculture. —Daryl Austin, USA Today, 22 Apr. 2025

However, certain medical conditions can cause low phosphorus levels.21 Magnesium and phosphorus can help:210 Maintain and improve bone health: Magnesium and phosphorus can increase bone mineral density (strength), help maintain bone breakdown and growth, and lower the risk of fractures. —Kirstyn Hill, Pharmd, Mph, Health, 22 Apr. 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