Atom

1. An ultimate indivisible particle of matter.
2. A constituent particle of matter, or a molecule supposed to be made up of subordinate particles.
3. The smallest particle of matter that can enter into combination; one of the elementary constituents of a molecule.
4. To reduce to atoms.
5. Anything extremely small; a particle; a whit.
6. An ultimate particle of matter not necessarily indivisible; a molecule.