deuterium
noun
deu·te·ri·um
dü-ˈtir-ē-əm 
also dyü-
: an isotope of hydrogen that has one proton and one neutron in its nucleus and that has twice the mass of ordinary hydrogen
—symbol D
called also heavy hydrogen
Examples of deuterium in a Sentence
Recent Examples on the Web
Helion’s fusion fuel combines deuterium from water with tritium.
—
Jordan Blum, Fortune, 13 Feb. 2026
While working on Copernicus, York was the first researcher to find an isotope of hydrogen known as deuterium inside these clouds.
—Bob Goldsborough, Chicago Tribune, 7 Feb. 2026
Operating since 1997, the reactor used deuterium and tritium as fuel and achieved record-breaking energy outputs during its nearly 25 years of operation.
—Ameya Paleja, Interesting Engineering, 27 Jan. 2026
The first-ever project to demonstrate the deuterium-tritium fuel cycle—the most viable route to practical fusion energy—plans to be operational by late 2026.
—IEEE Spectrum, 31 Dec. 2025
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Jordan Blum, Fortune, 13 Feb. 2026
While working on Copernicus, York was the first researcher to find an isotope of hydrogen known as deuterium inside these clouds.
—Bob Goldsborough, Chicago Tribune, 7 Feb. 2026
Operating since 1997, the reactor used deuterium and tritium as fuel and achieved record-breaking energy outputs during its nearly 25 years of operation.
—Ameya Paleja, Interesting Engineering, 27 Jan. 2026
The first-ever project to demonstrate the deuterium-tritium fuel cycle—the most viable route to practical fusion energy—plans to be operational by late 2026.
—IEEE Spectrum, 31 Dec. 2025
See All Example Sentences for deuterium
Cite this Entry
“Deuterium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/deuterium. Accessed 15 Feb. 2026.
Copy CitationKids Definition
deuterium
noun
deu·te·ri·um
d(y)ü-ˈtir-ē-əm
: the hydrogen isotope that is twice the mass of ordinary hydrogen
called also heavy hydrogen
Medical Definition
deuterium
noun
deu·te·ri·um
d(y)ü-ˈtir-ē-əm
: an isotope of hydrogen that has one proton and one neutron in its nucleus and that has twice the mass of ordinary hydrogen
called also heavy hydrogen
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