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

Then, Lebanon Utilities must seek a final permit through IDEM, which could dictate limits for contaminants like organic waste, heavy metals, phosphorus and ammonia. —Sophie Hartley, IndyStar, 20 Jan. 2026

Almond butter has more than five times the calcium as peanut butter, and more iron, magnesium, phosphorus, potassium, and vitamin E, says Guevara. —Kirsten Nunez, Martha Stewart, 17 Jan. 2026

The breakthrough was the development of solid-state lasers that use bundles of glass fibers doped with exotic elements like ytterbium, erbium, and thulium along with aluminum, germanium, and phosphorus. —New Atlas, 17 Jan. 2026

Here, nitrogen and phosphorus are scarce, and normal photosynthesis alone doesn’t cut it. —Scott Travers, Forbes.com, 16 Jan. 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