/i rup"sheuhn/ , n.
1. a breaking or bursting in; a violent incursion or invasion.
2. Ecol. a sudden increase in an animal population.
[ 1570-80; irruption- (s. of irruptio ), equiv. to irrupt ( us ), ptp. of irrumpere to burst into (see IR- 1 , RUPTURE) + -ion- -ION ]