thermonuclear

Of, or relating to the fusion of atomic nuclei at high temperatures.

The first thermonuclear reaction was in a star; it was brought about by heat, as the description implies.

Of, or relating to the use of atomic weapons based on such fusion, especially as distinguished from those based on fission.

I can't believe you gave me, a ten-year-old boy, a thermonuclear device [...]

A thermonuclear weapon.

China detonated her first thermonuclear in June 1967.