Lewis & Short

irruptĭo, ōnis, f. [irrumpo], a breaking or bursting in, an irruption.

  1. I. In gen.: irruptionem facere in popinam, Plaut. Poen. prol. 42: ferarum, Plin. Pan. 81: belli, Flor. 2, 12, 5: luminis, Pall. 10, 17: aquarum, Sen. Q. N. 3, 30, 5.
  2. II. Esp., as milit. t. t., an invasion, incursion, sally: hostis, Suet. Tib. 6: etiamsi irruptio facta nulla sit, Cic. de Imp. Pomp. 6, 15: Gallorum, Aug. Civ. Dei, 3, 31.