v.intr. 1 break out suddenly or dramatically. 2 (of a volcano) become active and eject lava etc. 3 a (of a rash, boil, etc.) appear on the skin. b (of the skin) produce a rash etc. 4 (of the teeth) break through the gums in normal development. eruption n. eruptive adj.
[ L erumpere erupt- (as E-, rumpere break) ]