an object of dread or apprehension; "Germany was always a bugbear for France"; "A foolish consistency is the hobgoblin of little minds"--Ralph Waldo Emerson
an acute viral disease of the nervous system of warm-blooded animals (usually transmitted by the bite of a rabid animal); rabies is fatal if the virus reaches the brain
march aggressively into another's territory by military force for the purposes of conquest and occupation; "Hitler invaded Poland on September 1, 1939"
penetrate or assault, in a harmful or injurious way; "The cancer had invaded her lungs"
occupy in large numbers or live on a host; "the Kudzu plant infests much of the South and is spreading to the North"
throw into great confusion or disorder; "Fundamental Islamicists threaten to perturb the social order in Algeria and Egypt"
disturb in mind or make uneasy or cause to be worried or alarmed; "She was rather perturbed by the news that her father was seriously ill"
cause a celestial body to deviate from a theoretically regular orbital motion, especially as a result of interposed or extraordinary gravitational pull; "The orbits of these stars were perturbed by the passings of a comet"
disturb or interfere with the usual path of an electron or atom; "The electrons were perturbed by the passing ion"