Nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter; a modern thermonuclear weapon weighing little more than a thousand kilograms can produce an explosion comparable to the detonation of more than a billion kilograms of conventional high explosive.Even small nuclear devices can devastate a city. Nuclear weapons are considered weapons of mass destruction, and their use and control has been a major aspect of international policy since their debut.

核武器。

nuclear是核子的意思。

weapon是武器的意思。

加起来就是核子武器，简称核武。