atom

n. [ L. atomus, Gr. &unr_;, uncut, indivisible; 'a priv. + &unr_;, verbal adj. of &unr_; to cut: cf. F. atome. See Tome. ] 1. (Physics) (a) An ultimate indivisible particle of matter. (b) An ultimate particle of matter not necessarily indivisible; a molecule. (c) A constituent particle of matter, or a molecule supposed to be made up of subordinate particles. [ 1913 Webster ]

☞ These three definitions correspond to different views of the nature of the ultimate particles of matter. In the case of the last two, the particles are more correctly called molecules. Dana. [ 1913 Webster ]

2. (Chem.) The smallest particle of matter that can enter into combination; one of the elementary constituents of a molecule. [ 1913 Webster ]

3. Anything extremely small; a particle; a whit. [ 1913 Webster ]

There was not an atom of water. Sir J. Ross. [ 1913 Webster ]

v. t. To reduce to atoms. [ Obs. ] Feltham. [ 1913 Webster ]

{ } 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 ]

adv. In an atomic manner; in accordance with the atomic philosophy. [ 1913 Webster ]

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 ]

n. An atomist. [ R. ] [ 1913 Webster ]

n. Atomism. [ Obs. ] [ 1913 Webster ]

n. [ Cf. F. atomicité. ] (Chem.) Degree of atomic attraction; equivalence; valence; also (a later use) the number of atoms in an elementary molecule. See Valence. [ 1913 Webster ]

n. 1. separating something into fine particles.
Syn. -- atomization, fragmentation [ WordNet 1.5 ]

2. annihilation by reducing something to atoms.
Syn. -- atomization [ WordNet 1.5 ]