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:

Atomic \A*tom"ic\, Atomical \A*tom"ic*al\, a. [Cf. F. atomique.]
   1. Of or pertaining to atoms.
      [1913 Webster]

   2. Extremely minute; tiny.
      [1913 Webster]

   Atomic bomb, see atom bomb in the vocabulary.

   Atomic philosophy, or Doctrine of atoms, a system which,
      assuming that atoms are endued with gravity and motion,
      accounted thus for the origin and formation of all things.
      This philosophy was first broached by Leucippus, was
      developed by Democritus, and afterward improved by
      Epicurus, and hence is sometimes denominated the Epicurean
      philosophy.

   Atomic theory, or the Doctrine of definite proportions
      (Chem.), teaches that chemical combinations take place
      between the supposed ultimate particles or atoms of
      bodies, in some simple ratio, as of one to one, two to
      three, or some other, always expressible in whole numbers.


   Atomic weight (Chem.), the weight of the atom of an element
      as compared with the weight of the atom of hydrogen, taken
      as a standard.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Atom bomb \At"om bomb`\, Atomic bomb \A*tom"ic bomb`\n.
   a bomb of great power in which the explosive energy is
   derived from the nuclear fission of a fissionable material,
   such as plutonium or uranium-235. It is a type of nuclear
   weapon. The strength of an atom bomb is measured in kilotons,
   i.e. the equivalent energy released by explosion of a
   thousand tons of TNT. The first atomic bomb was manufactured
   in 1945.

   Syn: A-bomb, fission bomb.
        [PJC] Atomic

WordNet (r) 3.0 (2006):

atomic bomb
    n 1: a nuclear weapon in which enormous energy is released by
         nuclear fission (splitting the nuclei of a heavy element
         like uranium 235 or plutonium 239) [syn: atom bomb,
         atomic bomb, A-bomb, fission bomb, plutonium bomb]