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

An organic fertilizer that is high in phosphorus helps assure a good flowering rate and strong stems. —Mary Marlowe Leverette, Southern Living, 9 July 2025

Fertilizer, compost, and aged manure contain valuable nutrients that plants need to grow, including the NPK macronutrients—nitrogen, potassium, and phosphorus—that help plants produce cells and influence how nutrients are transported within the plant. —Lauren Landers, Better Homes & Gardens, 7 July 2025

In addition, 3 ounces of liver provides 25 g of protein, 5 mg of iron, 422 mg of phosphorus, 299 mg of potassium, and 215 mcg of folate.8 7. —Ashley Braun, Verywell Health, 1 July 2025

The main sources of harmful algal blooms are excess nutrients in the water, typically phosphorus and nitrogen. —Gregory J. Dick, The Conversation, 26 June 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