atom
at.om \'at-*m\ n [ME, fr. L atomus, fr. Gk atomos, fr. atomos indivisible, fr.] a- + temnein to cut - more at TOME 1: one of the minute indivisible particles of which according to ancient ma terialism the universe is composed 2: a tiny particle : BIT 3a: the smallest particle of an element that can exist either alone or in combination 3b: a group of such particles constituting the smallest quantity of a radical 4: the atom considered as a source of vast potential energy