perturbation

noun3

1. •
   Agitation; the state of being perturbed.

   • Restore your selues, vnto your temper, Fathers; / And, vvithout perturbation, heare me speake: […] — 1611
2. •
   A small change in a physical system, or more broadly any definable system (such as a biological or economic system).
3. •
   Variation in an orbit due to the influence of external bodies.