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.
2. Extremely minute; tiny.
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
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.