(born c. 460died c. 370 BC) Greek philosopher. Though only a few fragments of his work survive, he was apparently the first to describe invisible atoms as the basis of all matter. His atomsindestructible, indivisible, incompressible, uniform, and differing only in size, shape, and motionanticipated with surprising accuracy those discovered by 20th-century scientists. For his amusement at human foibles, he has been called the Laughing Philosopher. See alsoatomism.