plutonium

noun

plu·​to·​ni·​um plü-ˈtō-nē-əm 

: a radioactive metallic element similar chemically to uranium that is formed as the isotope 239 by decay of neptunium and found in minute quantities in pitchblende, that undergoes slow disintegration with the emission of an alpha particle to form uranium 235, and that is fissionable with slow neutrons to yield atomic energy see Chemical Elements Table

Examples of plutonium in a Sentence

Recent Examples on the Web

All of this will be powered by a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) that converts the heat of decaying plutonium into electricity; this is commonly used on deep-space missions. —Phil Plait, Scientific American, 10 Apr. 2026

During reprocessing, spent nuclear fuel is separated to recover uranium and plutonium to recycle it for use in new fuel. —James Brooks, Los Angeles Times, 9 Apr. 2026

During reprocessing, spent nuclear fuel is separated to recover uranium and plutonium to recycle it for use in new fuel. —ABC News, 8 Apr. 2026

Starring Chris Pratt as Mario, Charlie Day as Luigi, and Jack Black as Bowser, the new take on the Mario movie packed more (intentionally) comedic weight and was kid-friendly, weapons-grade plutonium at the box office. —Christopher Cruz, Rolling Stone, 5 Apr. 2026

Word History

Etymology

New Latin, from Pluton-, Pluto, the planet Pluto

First Known Use

1942, in the meaning defined above

Rhymes for plutonium

• carbonium
• harmonium
• meconium
• polonium
• stramonium
• zirconium
• conium
• diazonium
• pandemonium
• pelargonium
• testimonium

Kids Definition

plutonium

noun

plu·​to·​ni·​um plü-ˈtō-nē-əm 

: a radioactive metallic element that is formed by decay of neptunium and found in minute quantities in pitchblende and that produces atomic energy by fission see element

Medical Definition

plutonium

noun

plu·​to·​ni·​um plü-ˈtō-nē-əm 

: a radioactive metallic element similar chemically to uranium that is formed as the isotope 239 by decay of neptunium and found in minute quantities in pitchblende, that undergoes slow disintegration with the emission of an alpha particle to form uranium 235, and that is fissionable with slow neutrons to yield atomic energy

—symbol Pu see Chemical Elements Table