plutonium

American  

[ploo-toh-nee-uhm] / pluˈtoʊ ni əm /

noun

Chemistry, Physics.

1. a transuranic element with a fissile isotope of mass number 239 plutonium 239 that can be produced from non-fissile uranium 238, as in a breeder reactor. Pu; 94.

---

plutonium British  

/ pluːˈtəʊnɪəm /

noun

1. a highly toxic metallic transuranic element. It occurs in trace amounts in uranium ores and is produced in a nuclear reactor by neutron bombardment of uranium-238. The most stable and important isotope, plutonium-239 , readily undergoes fission and is used as a reactor fuel in nuclear power stations and in nuclear weapons. Symbol: Pu; atomic no: 94; half-life of ²³⁹ Pu: 24 360 years; valency: 3, 4, 5, or 6; relative density (alpha modification): 19.84; melting pt: 640°C; boiling pt: 3230°C

---

plutonium Scientific  

/ plo̅o̅-tō′nē-əm /

1. A silvery, radioactive metallic element of the actinide series that has the highest atomic number of all naturally occurring elements. It is found in minute amounts in uranium ores and is produced artificially by bombarding uranium with neutrons. It is absorbed by bone marrow and is highly poisonous. Plutonium is used in nuclear weapons and as a fuel in nuclear reactors. Its longest-lived isotope is Pu 244 with a half-life of 80 million years. Atomic number 94; melting point 640°C; boiling point 3,228°C; specific gravity 19.84; valence 3, 4, 5, 6.

2. See Periodic Table

---

plutonium Cultural  

1. A radioactive chemical element that is artificially derived from uranium.

---

Discover More

Plutonium is used in nuclear reactors.

Etymology

Origin of plutonium

1940–45; < Greek Ploútōn Pluto + -ium

---

Compare meaning

How does plutonium compare to similar and commonly confused words? Explore the most common comparisons:

• plutonium vs. uranium

---

Example Sentences

See Examples For:

plutonium

As that plutonium supply steadily diminishes, each spacecraft loses about 4 watts of available power every year.

From Science Daily ● Aug. 10, 2026

I mean, the idea that we need to build new plutonium pits, meaning new triggers for nuclear weapons, is utterly ridiculous.

From Salon ● Jun. 15, 2026

It would run on mixed-oxide fuel, made from plutonium recovered from used reactor fuel and surplus government stockpiles, mixed with depleted uranium.

From The Wall Street Journal ● May 27, 2026

The government has designated roughly 50 metric tons of plutonium as weapons-grade but excessive to national security needs.

From Barron's ● May 26, 2026

Whether the plutonium bomb worked or not, the plan was to have one uranium bomb assembled and ready for use by early August.

From "Bomb" by Steve Sheinkin

Random Word

Spin the wheel and learn a new word!

---