thermonuclear

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."