The Collaborative International Dictionary of English v.0.48:

Nuclear weapon \Nu"cle*ar wea"pon\, n.
   A weapon of great explosive power, such as an atomic bomb
   or a hydrogen bomb, which depends for most of its explosive
   power on the release of energy from within atomic nuclei by a
   nuclear reaction. A fission weapon or a fusion weapon.
   The term includes atomic shells for cannon.
   [PJC]