an issuing forth suddenly and violently; outburst; outbreak.

Geology . the ejection of molten rock, steam, etc., as from a volcano or geyser.

something that is erupted or ejected, as molten rock, volcanic ash, or steam.

Pathology .

the breaking out of a rash or the like.

a rash or exanthem.

noun

access , blast , blow-up , breakout , burst , discharge , explosion , flare-up , flow , gust , outbreak , outburst , sally , venting , vomitingnotes:eruption is breaking out; irruption is breaking in , blowup , fit , commotion , efflorescence , ejection , exanthema , inflammation , outpouring , rash , rush , storm