/in vay"zheuhn/ , n.
1. an act or instance of invading or entering as an enemy, esp. by an army.
2. the entrance or advent of anything troublesome or harmful, as disease.
3. entrance as if to take possession or overrun: the annual invasion of the resort by tourists.
4. infringement by intrusion.
[ 1400-50; late ME invasion- (s. of invasio ), equiv. to invas ( us ), ptp. of invadere + -ion- -ION; see INVADE ]