Atom

Part of speech: noun (n.)

1. An ultimate indivisible particle of matter.

2. An ultimate particle of matter not necessarily indivisible; a molecule.

3. A constituent particle of matter, or a molecule supposed to be made up of subordinate particles.

4. The smallest particle of matter that can enter into combination; one of the elementary constituents of a molecule.

5. Anything extremely small; a particle; a whit. There was not an atom of water. Sir J. Ross.

Part of speech: verb (v.)

To reduce to atoms. [Obs.] Feltham.