"to break into," 1805 (implied in irrupted), back-formation from irruption or else from Latin irruptus, past participle of irrumpere "to break in, burst into."

1570s, from French irruption (14c.) or directly from Latin irruptionem (nominative irruptio) "a breaking in, bursting in, invasion," noun of action from past-participle stem of irrumpere "to break in, force one's way in, burst into," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + rumpere (see rupture (n.)). Frequently confused with eruption.