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.
(history of science) A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter.
The smallest, indivisible constituent part or unit of something.
In logical atomism, a fundamental fact that cannot be further broken down.
The smallest medieval unit of time, equal to fifteen ninety-fourths of a second.
A mote of dust in a sunbeam.
A very small amount; a whit.
(Lisp) An individual number or symbol, as opposed to a list; a scalar value.
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 that has only zero below it.
An element of a set that is not itself a set; an urelement.
(usually capitalised as "Atom") A member of an age group division in hockey for ten- to 11-year-olds.