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

In the beginning, use a nitrogen-rich fertilizer for the seedlings before switching to one with phosphorus and potassium after the plants have started to sprout. — Ashlyn Needham, Southern Living, 26 June 2026

Pork loin is also rich in protein, phosphorus, and selenium. — Mark Gurarie, Health, 25 June 2026

Livestock produce manure that is high in both nitrogen and phosphorus, which makes excellent fertilizer. — Nandita Basu, The Conversation, 24 June 2026

All bodies of stagnant water are particularly vulnerable to a process known as eutrophication (the gradual increase in the concentration of plant nutrients such as phosphorus and nitrogen), and the Reflecting Pool is no exception. — Tracy Grant, Encyclopedia Britannica, 23 June 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