(1):
(n.) The act of invading; the act of encroaching upon the rights or possessions of another; encroachment; trespass.
(2):
(n.) The incoming or first attack of anything hurtful or pernicious; as, the invasion of a disease.
(3):
(n.) A warlike or hostile entrance into the possessions or domains of another; the incursion of an army for conquest or plunder.