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

Multi-Version Concordance Atom (1 Occurrence) Isaiah 40:15 Behold, the nations are esteemed as a drop of the bucket, and as the fine dust on the scales; behold, he taketh up the isles as an atom. (DBY)