RELATIVITY

noun (plural -ties) Date: circa 1834 1. the quality or state of being relative, something that is relative, the state of being dependent for existence on or determined in nature, value, or quality by relation to something else, 3. a theory which is based on the two postulates (1) that the speed of light in a vacuum is constant and independent of the source or observer and (2) that the mathematical forms of the laws of physics are invariant in all inertial systems and which leads to the assertion of the equivalence of mass and energy and of change in mass, dimension, and time with increased velocity, an extension of the theory to include gravitation and related acceleration phenomena, relativism 1b