PERTURBATION

n. 1 the act or an instance of perturbing; the state of being perturbed. 2 a cause of disturbance or agitation. 3 Physics a slight alteration of a physical system, e.g. of the electrons in an atom, caused by a secondary influence. 4 Astron. a minor deviation in the course of a celestial body, caused by the attraction of a neighbouring body.