<p><strong>Noun</strong></p><ul><li>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.</li><li>an atom with one of the electrons replaced by some other particle: muonic atom; kaonic atom.</li><li>Energy. this component as the source of nuclear energy.</li><li>a hypothetical particle of matter so minute as to admit of no division.</li><li>anything extremely small; a minute quantity.</li><li>Synonyms: whit, jot, iota, scintilla, speck, shred.</li></ul>