- designating or of a reaction in which isotopes of a light element, esp. hydrogen, fuse at temperatures of millions of degrees into heavier nuclei
- designating, of, or employing the heat energy released in nuclear fusion: thermonuclear reactor
Origin of thermonuclearthermo- + nuclear
- Relating to or derived from the fusion of atomic nuclei at high temperatures: thermonuclear reactions.
- Relating to or characterized by the use of weapons that employ nuclear fusion, especially as distinguished from those that employ only nuclear fission: thermonuclear war.