atom /at″əm/ [Gk, atmos, indivisible] , 1. (in chemistry and physics) the smallest division of an element that exhibits all the properties and characteristics of the element. It comprises neutrons, electrons, and protons. The number of protons in the nucleus of every atom of any given element is the same and is called its atomic number. 2. (Nontechnical) the amount of any substance that is so small that further division is not possible. −atomic, adj.
