An Etymological Dictionary of Astronomy and Astrophysics

1. Any departure introduced into a steady state of a system.
   The magnitude is often assumed to be small so that the resulting terms in the dependent variables may be neglected. The term “perturbation” is therefore sometimes used as synonymous with “small perturbation.”
   

2. Gravitational effect of a third body that causes an alteration in the orbit of a body going around its primary.
   

See also:

→ linear perturbation theory, → method of small perturbationsn → perturbation equation, → perturbation method, → primordial curvature perturbation, → scalar perturbation, → secular perturbation, → tensor perturbation, → vector perturbation.

See also: Verbal noun of → perturb.