[From Greek atomos: indivisible.]
(metaphysics) Any metaphysical or cosmological idea that reality is fundamentally made up of extremely small, indivisible particles. This view was widespread among ancient Greek philosophers such as Democritus (c. 460 - c. 370 BCE) and Epicurus (341-270 BCE), and was revived in modern times by philosophers such as Pierre Gassendi (1592-1655) and scientists such as Robert Boyle (1627-1691), the founder of modern chemistry.