early 15c., erupcioun, from Old French éruption (14c.) and directly from Latin eruptionem (nominative eruptio) "a breaking out," noun of action from past-participle stem of erumpere "break out, burst forth," from assimilated form of ex "out" (see ex-) + rumpere "to break, rupture" (see rupture (n.)).

1570s, from French irruption (14c.) or directly from Latin irruptionem (nominative irruptio) "a breaking in, bursting in, invasion," noun of action from past-participle stem of irrumpere "to break in, force one's way in, burst into," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + rumpere (see rupture (n.)). Frequently confused with eruption.

"disturbance, disorderly dispute," 1825, a dialectal or colloquial word of unknown origin. Perhaps from eruption or an altered shortening of insurrection.

"eruption, a sudden and violent manifestation" (of disease, hostilities, etc.), c. 1600, from the verbal phrase; see out (adv.) + break (v.). Outbreak (v.) "to break out, escape confinement" (c. 1300) was still in poetic use in 19c.

pustular disease of the skin, late 14c., from Latin impetigo "skin eruption," from impetere "to attack" (see impetus). Originally used generally; the sense narrowed in modern times to specific diseases. Related: Impetiginous.

1650s, from Latin vitiligo "a kind of cutaneous eruption, tetter" (Celsus), perhaps with an original sense of "blemish," from PIE *wi-tu-, from root *wei- (3) "vice, fault, guilt" (see vice (n.1)).

"affection of the skin characterized by simple itching without visible eruption," 1650s, from Latin pruritus, past participle of prurire "to itch" (see prurient). The word was earlier in English via Old French in form prurite (early 15c.). Related: Pruritic.

skin eruption common during puberty, 1813, from Modern Latin, from aknas, a 6c. Latin clerical misreading of Greek akmas, accusative plural of akmē "point" (see acme), from PIE root *ak- "be sharp, rise (out) to a point, pierce." The "pointed" pimples are the source of the medical use.

in geology, "formed by volcanic agencies," especially in reference to fast-moving, dense, superheated surges of ash, gas and rock in a volcanic eruption; by 1862 in reference to the rocks that result; see pyro- "fire" + clastic, indicating "broken in pieces, fragments."

The word "ash" is not a very good one to include all the mechanical accompaniments of a subaerial or subaqueous eruption, since ash seems to be restricted to a fine powder, the residuum of combustion. A word is wanting to express all such accompaniments, no matter what their size and condition may be, when they are accumulated in such mass as to form beds of "rock." We might call them perhaps "pyroclastic materials," but I have endeavoured in vain to think of an English word which should express this meaning, and believe, therefore, that the only plan will be to retain the word "ash," giving it an enlarged technical meaning, so as to include all the fragments accumulated during an igneous eruption, no matter what size or what shape they may be. [J. Beete Jukes, "The Student's Manual of Geology," Edinburgh, 1862]

late 14c., "any inflammatory, spreading skin condition" (used of shingles, gangrene, etc.), from Latin herpes "a spreading skin eruption," from Greek herpes, the name for the disease shingles, literally "creeping," from herpein "to creep, move slowly" (cognate with Latin serpere "to creep;" see serpent). The condition was not distinguished into specific diseases until early 19c.