Origin and history of egress

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-.

Proto-Indo-European root meaning "to walk, go." 

It might form all or part of: aggress; aggression; aggressive; centigrade; congress; degrade; degree; degression; digress; digression; egress; gradation; grade; gradual; graduate; grallatorial; gravigrade; ingredient; ingress; plantigrade; progress; progression; regress; regression; retrograde; retrogress; tardigrade; transgress; transgression.

It might also be the source of: Latin gradus "a step, a pace, gait," figuratively "a step toward something, a degree of something rising by stages;" gradi "to walk, step, go;" Lithuanian gridiju, gridyti "to go, wander;" Old Church Slavonic gredo "to come;" Old Irish in-greinn "he pursues."