from the GNU version of the Collaborative International Dictionary of English
- n. an explosive device, whether used as a weapon or for other purposes, which depends for most of its explosive power on the release of energy from within atomic nuclei. A fission device or a fusion device.
Sorry, no etymologies found.
But even a group armed with such scientific knowledge would still have to overcome enormous technical challenges to build a workable nuclear device or to weaponize agents such as anthrax.
So, even building the simple gun-type nuclear device of the kind that was dropped on Hiroshima would be extraordinarily difficult for a terrorist group because of the problem of accumulating sufficient quantities of HEU.