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
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In fact, in 2014, Japan already possessed 9 tons of plutonium, which would be enough to create around 5,000 nuclear bombs.
—
Christopher McFadden, Interesting Engineering, 28 Dec. 2025
Those who believe that the U.S. needs to reestablish mass production of plutonium pits cite the potential for a three-way arms race between the U.S., Russia and China once the world's last arms control treaty expires in February 2026.
—Davis Winkie, USA Today, 16 Dec. 2025
During World War II and throughout the Cold War, the Hanford reactors along the Columbia River near Richland, Washington produced most of the plutonium in the US arsenal of bombs and missiles, leaving behind 56 million gallons of radioactive sludge stored in 177 aging underground tanks.
—New Atlas, 14 Dec. 2025
Fission works by splitting heavy atoms such as uranium or plutonium to release energy – a principle used in most terrestrial nuclear reactors.
—Preeti Nair, Space.com, 7 Dec. 2025
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Christopher McFadden, Interesting Engineering, 28 Dec. 2025
Those who believe that the U.S. needs to reestablish mass production of plutonium pits cite the potential for a three-way arms race between the U.S., Russia and China once the world's last arms control treaty expires in February 2026.
—Davis Winkie, USA Today, 16 Dec. 2025
During World War II and throughout the Cold War, the Hanford reactors along the Columbia River near Richland, Washington produced most of the plutonium in the US arsenal of bombs and missiles, leaving behind 56 million gallons of radioactive sludge stored in 177 aging underground tanks.
—New Atlas, 14 Dec. 2025
Fission works by splitting heavy atoms such as uranium or plutonium to release energy – a principle used in most terrestrial nuclear reactors.
—Preeti Nair, Space.com, 7 Dec. 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 31 Dec. 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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