"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."
She irrupted into our sitting room
The crowd irrupted into a burst of patriotism
The island's rodent population irrupted
irritant
irritate
irritating
irritation
irrumation
irrupt
irruption
IRS
Irwin
is
Isaac
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