[per.tur.ba.tion] n (14c) 1: the action of perturbing: the state of being perturbed
2: a disturbance of motion, course, arrangement, or state of equilibrium; esp: a disturbance of the regular and usu. elliptical course of motion of a celestial body that is produced by some force additional to that which causes its regular motion -- per.tur.ba.tion.al adj