thermonuclear

What it means

1. not comparableOf, 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.

   1956 May 25, “Chances Of Power Station Use For Hydrogen Bomb”, in The Times, London

2. not comparableOf, 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 [...]

   2021 January 30, ISP, quoting iSorrowproductions, Beating Fallout 3 But Every Enemy Has A NUKE - Every Enemy Has A Fat Man Mod

In a sentence

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

1956 May 25, “Chances Of Power Station Use For Hydrogen Bomb”, in The Times, London

Where it comes from

1. Proto-Indo-European*gʷʰer-
2. Proto-Indo-European*gʷʰermos
3. Proto-Hellenic*kʷʰermós
4. Ancient Greekθερμός (thermós)
5. Englishthermo-
6. Englishnuclear
7. Englishthermonuclear

From thermo- + nuclear.