adventitious (adj.)

"important arrival," 1742, an extended sense of Advent "season preceding Christmas" (in reference to the "coming" of Christ), which was in late Old English, from Latin adventus "a coming, approach, arrival," in Church Latin "the coming of the Savior," from past participle of advenire "arrive at, come to," from ad "to" (see ad-) + venire "to come" (from a suffixed form of PIE root *gwa- "to go, come"). Related: Adventual.

*gwā-, also *gwem-, Proto-Indo-European root meaning "to go, come."

It forms all or part of: acrobat; adiabatic; advent; adventitious; adventure; amphisbaena; anabasis; avenue; base (n.) "bottom of anything;" basis; become; circumvent; come; contravene; convene; convenient; convent; conventicle; convention; coven; covenant; diabetes; ecbatic; event; eventual; hyperbaton; hypnobate; intervene; intervenient; intervention; invent; invention; inventory; juggernaut; katabatic; misadventure; parvenu; prevenient; prevent; provenance; provenience; revenant; revenue; souvenir; subvention; supervene; venire; venue; welcome.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gamati "he goes," Avestan jamaiti "goes," Tocharian kakmu "come," Lithuanian gemu, gimti "to be born," Greek bainein "to go, walk, step," Latin venire "to come," Old English cuman "come, approach," German kommen, Gothic qiman.