perturbation

Etymology

Borrowed from Middle French perturbation, from Old French perturbacion, from Latin perturbatio.

noun

1. (uncountable) Agitation; the state of being perturbed
   But her mind had never been in such perturbation; and it needed a very strong effort to appear attentive and cheerful till the usual hour of separating allowed her the relief of quiet reflection. 1815, Jane Austen, Emma, volume I, chapter 5
2. (countable) A small change in a physical system, or more broadly any definable system (such as a biological or economic system)
3. (countable, astronomy, physics) Variation in an orbit due to the influence of external bodies