Plutonium (noun)

A radioactive metallic element of the actinide series, occurring naturally only in trace amounts, with the atomic number 94. It is produced artificially for use as a fuel in nuclear reactors and as a source of weapons-grade material.

Origin:

1940s: from plut(o) + -onium, after the planet pluto.

Examples:

1. The use of plutonium in nuclear weapons has been controversial.
2. Plutonium is used as a fuel for nuclear reactors.
3. The disposal of plutonium waste is a major challenge.
4. Plutonium is a very dense element.
5. Plutonium is highly toxic and radioactive.