Perturbation /(?)/

Per·tur·ba·tion

Perturbation

n.
  1. The act of perturbing, or the state of being perturbed; esp., agitation of mind.
  2. A disturbance in the regular elliptic or other motion of a heavenly body, produced by some force additional to that which causes its regular motion; as, the perturbations of the planets are caused by their attraction on each other. (Astron.)