perturbation

1. (uncountable) Agitation; the state of being perturbedExamples: "Reſtore your ſelues, vnto your temper, Fathers; / And, vvithout perturbation, heare me ſpeake: […]"; "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."uncountable

2. (countable) A small change in a physical system, or more broadly any definable system (such as a biological or economic system)Examples: "Natures that haue much Heat, and great and violent deſires and Perturbations, are not ripe for Action, till they haue paſſed the Meridian of their yeares: As it was with Iulius Cæſar, and Septimius Seuerus."countable

3. (countable, astronomy, physics) Variation in an orbit due to the influence of external bodiescountable