| atom | |
| 1. n. (chemistry, physics) The smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons. | |
| 2. n. (history of science) A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter. | |
| 3. n. (now generally regarded figuratively) The smallest, indivisible constituent part or unit of something. | |
| 4. n. (now historical) The smallest medieval unit of time, equal to fifteen ninety-fourths of a second. | |
| 5. n. A mote of dust in a sunbeam. | |
| 6. n. A very small amount; a whit. | |
| 7. n. (computing, programming, Lisp) An individual number or symbol, as opposed to a list; a scalar value. | |
| 8. n. (mathematics, algebra) A non-zero member of a Boolean algebra that is not a union of any other elements. Or, a non-zero member of a Boolean lattice which contains only the zero and itself. | |
| In a Venn diagram, an atom is depicted as an area circumscribed by lines but not cut by any line. | |
| 9. n. (mathematics, set theory) An element of a set that is not itself a set; an urelement. | |
