1630s, "to plunge or sink in" (to something), a sense now obsolete, from Latin mergere "to dip, dip in, immerse, plunge," probably rhotacized from *mezgo, from PIE *mezgo- "to dip, to sink, to wash, to plunge" (source also of Sanskrit majjanti "to sink, dive under," Lithuanian mazgoju, mazgoti, Latvian mazgat "to wash").

Intransitive meaning "sink or disappear into something else, be swallowed up, lose identity" is from 1726, in the specific legal sense of "absorb an estate, contract, etc. into another." Transitive sense of "cause to be absorbed or to disappear in something else" is from 1728. Related: Merged; merging. As a noun, from 1805.

1640s, "unforeseen occurrence, sudden change of condition," from French émergence, from emerger, from Latin emergere "rise up" (see emerge). The oldest English sense is now that of emergency (q.v.) and is obsolete in this word. The surviving meaning "an emerging, process of coming forth" (from concealment or obscurity) is attested by 1704 in astronomy and optics, in general use by 1755, perhaps directly from emerge. In reference to the rising of land from the water in geology, etc., by 1833.

"unforeseen occurrence requiring immediate attention," 1630s, from Latin emergens, present participle of emergere "to rise out or up" (see emerge). Or from emerge + -ency. As an adjective by 1881. Compare emergence, with which it was interchangeable into 19c.

In reference to a national or widespread uprising or military crisis, by 1860 in reference to the (looming) U.S. Civil War.

Emergency men. The term is as old as the War. The first call for seventy-five thousand men was for three months—for the emergency. Then Stuart conceived the idea of a pleasant little excursion into Pennsylvania, and we sent up Regiment after Regiment of "emergency men," just as the last tail of the last rebel horse was disappearing beyond the Potomac. [Newville, Pa. "Star of the Valley," Aug. 13, 1864]

late 14c., "rising from what surrounds it, coming into view," from Latin emergentem (nominative emergens), present participle of emergere "to rise out or up" (see emerge).

in botany, "standing out of or raised above water, raised partially above surrounding leaves," 1680s, formed as if a past-participle adjective, from Latin emersus, past participle of emergere "rise out or up" (see emerge).

"reappearance, act of emerging," 1630s, noun of action from past-participle stem of Latin emergere "to rise out or up" (see emerge). Originally of eclipses and occultations.

also reemerge, "to emerge again or anew," 1775; see re- "back, again" + emerge (v.). Related: Re-emerged; re-emerging; re-emergence (1801).

word-forming element, in English meaning usually "out of, from," but also "upwards, completely, deprive of, without," and "former;" from Latin ex "out of, out from the interior of a thing" (in opposition to in), "from within; from which time, since; according to; in regard to." This is reconstructed to be from PIE *eghs "out" (source also of Gaulish ex-, Old Irish ess-, Old Church Slavonic izu, Russian iz). In some cases also from Greek cognate ex, ek.

Often reduced to e- before -b-, -d-, -g-, consonantal -i-, -l-, -m-, -n-, -v- (as in elude, emerge, evaporate, etc.).

The sense in Latin naturally tended toward "thoroughly, utterly," and in some English ex- words with no clear connection to the idea of "out of," the element might be purely intensive. Among them are exhort, exhilarate, evident, excruciate, exclaim, exuberant, exaggerate, expiate, expect.

For use of Latin ex- as "(rise) up out of," as preserved in English emerge, emend, the notion is "out from the interior of a thing," in opposition to in-. Hence also in Latin, "in an upward direction," as in effervesce, exult, extol.

PIE *eghs had comparative form *eks-tero and superlative *eks-t(e)r-emo-.