[Revised entry by Sylvia Berryman on October 18, 2022. Changes to: Main text, Bibliography] A number of philosophical schools in different parts of the ancient world held that the universe is composed of some kind of 'atoms' or minimal parts, albeit for different reasons. Although the modern term 'atom' derives from the ancient Greek adjective atomos, which literally means 'uncuttable', it is possible that the first theories we can describe as atomist were developed in classical Indian philosophy. While the ancient Greeks from whom we derive the modern term were...