- Physics.
- the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.
- an atom with one of the electrons replaced by some other particle: muonic atom;kaonic atom.
- this component as the source of nuclear energy.
- a hypothetical particle of matter so minute as to admit of no division.
- anything extremely small; a minute quantity.
- the smallest quantity of an element that can take part in a chemical reaction
- this entity as a source of nuclear energy
- any entity regarded as the indivisible building block of a theory
- the hypothetical indivisible particle of matter postulated by certain ancient philosophers as the fundamental constituent of matter
- a very small amount or quantity; minute fragment
