Entry 3 senses Webster, 1913 Invasion /ĭnˌ-vāzh'-ən/ · In·va·sion · IPA /ɪnˈveɪʒən/ 01 n. The act of invading; the act of encroaching upon the rights or possessions of another; encroachment; trespass. 1. The act of invading; the act of encroaching upon the rights or possessions of another; encroachment; trespass. 2. A warlike or hostile entrance into the possessions or domains of another; the incursion of an army for conquest or plunder. 3. The incoming or first attack of anything hurtful or pernicious; as, the invasion of a disease. Syn. Invasion, Irruption, Inroad. Invasion is the generic term, denoting a forcible entrance into a foreign country. Incursion signifies a hasty and sudden invasion. Irruption denotes particularly violent invasion. Inroad is entry by some unusual way involving trespass and injury.