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]

The Collaborative International Dictionary of English v.0.48:

H-bomb \H"-bomb`\ ([=a]ch"b[o^]mb`) n.
   The hydrogen bomb, a thermonuclear weapon that releases
   atomic energy by union of hydrogen nuclei at high
   temperatures to form helium. The force of its explosion may
   range from one to hundreds of megatons of TNT equivalent.

   Syn: hydrogen bomb, fusion bomb, thermonuclear bomb.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

hydrogen bomb
    n 1: a nuclear weapon that releases atomic energy by union of
         light (hydrogen) nuclei at high temperatures to form helium
         [syn: hydrogen bomb, H-bomb, fusion bomb,
         thermonuclear bomb]