Pronunciation: (i-rup'shun),[key] —n. 1. an issuing forth suddenly and violently; outburst; outbreak.
2. Geol.the ejection of molten rock, steam, etc., as from a volcano or geyser.
3. something that is erupted or ejected, as molten rock, volcanic ash, or steam.
4. Pathol. a. the breaking out of a rash or the like.
b. a rash or exanthem.