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