thermonuclear

American  

[thur-moh-noo-klee-er, -nyoo-, -kyuh-ler] / ˌθɜr moʊˈnu kli ər, -ˈnyu-, -kyə lər /

adjective

1. of, relating to, or involving a thermonuclear reaction.

   thermonuclear power.

---

thermonuclear British  

/ ˌθɜːməʊˈnjuːklɪə /

adjective

1. involving nuclear fusion

   a thermonuclear reaction

   thermonuclear energy

2. involving thermonuclear weapons

   a thermonuclear war

---

thermonuclear Scientific  

/ thûr′mō-no̅o̅′klē-ər /

1. Relating to the fusion of atomic nuclei at high temperatures or to the energy produced in this way.

2. Relating to weapons based on nuclear fusion, especially as distinguished from those based on nuclear fission.

---

thermonuclear Cultural  

1. A term referring to devices that use nuclear fusion, the fusion of atomic nuclei, to produce energy at very high temperatures. (See hydrogen bomb.)

---

Pronunciation

See nuclear.

Etymology

Origin of thermonuclear

First recorded in 1935–40; thermo- + nuclear

Explanation

Something that has to do with high-temperature nuclear reactions is thermonuclear. Thermonuclear weapons are made using nuclear fusion. You'll almost always find the adjective thermonuclear describing the scientific process—it's a specific way to create fusion—or the resulting weapon. The word was first used around 1938 in reference to a process that occurs in stars. The first tests of a hydrogen bomb in the 1950s spawned the more common use of thermonuclear. The word combines the Greek thermos, "hot" and nuclear, "of the nucleus of a cell."

Example Sentences

Magnetic confinement devices—whether the doughnut-shaped tokamaks used in the International Thermonuclear Experimental Reactor project or the linear configuration pursued by TAE—rely on intricate magnetic fields to hold the plasma together.

From The Wall Street Journal • Dec. 28, 2025

"The lawsuit is here. Thermonuclear it is not," quipped attorney Bradley Moss.

From Salon • Nov. 21, 2023

Thermonuclear supernovae are explosive deaths of white dwarfs caused by runaway nuclear reactions.

From Scientific American • Jul. 4, 2023

One project working to demonstrate the feasibility of nuclear fusion is ITER, the International Thermonuclear Experimental Reactor.

From National Geographic • Jun. 11, 2023

Thermonuclear reactions in the solar interior support the outer layers of the Sun and postpone for billions of years a catastrophic gravitational collapse.

From "Cosmos" by Carl Sagan