1. to disturb or disquiet greatly in mind; agitate; unsettle.
2. to throw into great disorder; derange.
3. Astronomy: to cause perturbation in the orbit of (a celestial body).
Etymology: from Middle English perturben < Old French perturber < Latin perturbāre, “to throw into confusion”, equivalent to per-, prefix for “thoroughly; utterly” + turbāre, “to disturb”.