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
The assembly is designed for use in fourth-generation fast neutron reactors and features mixed nitride uranium-plutonium (SNUPP) fuel that incorporates a liquid metal sublayer.
—
Aman Tripathi, Interesting Engineering, 8 Oct. 2025
The agreement, ratified in 2011, required both nations to dispose of 34 tons of weapons-grade plutonium.
—Amanda Castro, MSNBC Newsweek, 8 Oct. 2025
Whether the vacuum is contaminated with helium or plutonium, the measured pressure will vary by perhaps only a few percent, while the ion gauge sensitivity and reading for these particles might differ by an order of magnitude, Eckel says.
—IEEE Spectrum, 24 Sep. 2025
The result was the 1994 Agreed Framework, which required that North Korea freeze the construction of nuclear reactors suspected of being used in weapons production and placed the country’s existing plutonium production capabilities under the IAEA inspection regime.
—Vipin Narang, Foreign Affairs, 5 Sep. 2025
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Aman Tripathi, Interesting Engineering, 8 Oct. 2025
The agreement, ratified in 2011, required both nations to dispose of 34 tons of weapons-grade plutonium.
—Amanda Castro, MSNBC Newsweek, 8 Oct. 2025
Whether the vacuum is contaminated with helium or plutonium, the measured pressure will vary by perhaps only a few percent, while the ion gauge sensitivity and reading for these particles might differ by an order of magnitude, Eckel says.
—IEEE Spectrum, 24 Sep. 2025
The result was the 1994 Agreed Framework, which required that North Korea freeze the construction of nuclear reactors suspected of being used in weapons production and placed the country’s existing plutonium production capabilities under the IAEA inspection regime.
—Vipin Narang, Foreign Affairs, 5 Sep. 2025
See All Example Sentences for plutonium
Cite this Entry
“Plutonium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/plutonium. Accessed 17 Oct. 2025.
Copy CitationKids 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
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