(purr-ter-BAY-shun), noun
Originally used to describe the phenomenon of one planet’s gravitational field throwing another planet’s orbit slightly out of kilter. Today, perturbation refers more generally to any disturbance that alters the normal state or function of a system, moving object, person, or process.
“O polished PERTURBATION! golden care! / That keep’st the ports of slumber open wide / To many a watchful night.” – William Shakespeare