An invasion is the movement of an army into a region, usually in a hostile attack that's part of a war or conflict. World history is full of descriptions of invasions.

One country's army plundering or taking over a city or piece of land in another country is an invasion. You can call other mass movements invasions as well, like a horrifying invasion of your kitchen by cockroaches, or the invasion of a stadium by excited soccer fans. A common phrase is "invasion of privacy," which means an unfair intrusion into someone's personal space or private information.

Definitions of invasion

n any entry into an area not previously occupied

“an invasion of tourists”
“an invasion of locusts”
encroachment, intrusion
Type of:
entering, entrance
a movement into or inward

n the act of invading; the act of an army that invades for conquest or plunder

an invasion or hostile attack
Type of:
incursion, penetration
an attack that penetrates into enemy territory

n (pathology) the spread of pathogenic microorganisms or malignant cells to new sites in the body

“the tumor's invasion of surrounding structures”
Type of:
spread, spreading
process or result of distributing or extending over a wide expanse of space

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