eftsoons adv.

also *ap-, Proto-Indo-European root meaning "off, away."

It forms all or part of: ab-; abaft; ablaut; aft; after; apanthropy; aperitif; aperture; apo-; apocalypse; apocryphal; Apollyon; apology; apoplexy; apostle; apostrophe; apothecary; apotheosis; awk; awkward; ebb; eftsoons; of; off; offal; overt.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit apa "away from," Avestan apa "away from," Greek apo "from, away from; after; in descent from," Latin ab "away from, from," Gothic af, Old English of "away from."

Middle English sone, from Old English sona "at once, immediately, directly, forthwith," from Proto-Germanic *sæno (source also of Old Frisian son, Old Saxon sana, Old High German san, Gothic suns "soon"). The sense relaxed early Middle English to "within a short time" (compare anon, just (adv.)).

Sooner or later "at some undetermined future time but inevitably" is by 1570s. American English Sooner for "Oklahoma native" is 1930 (earlier "one who acts prematurely," 1889), in reference to the 1889 opening to Americans of what was then part of Indian Territory, when many would-be settlers sneaked onto public land and staked their claims "sooner" than the legal date and time.

late Old English agan, from earlier ongean (prep.) "toward; opposite, against, contrary to; in exchange for," as an adverb "in the opposite direction, back, to or toward a former place or position," from on "on" (see on (prep.) and compare a- (1)) + -gegn "against, toward." This is from the Germanic root *gagina (source also of Old Norse gegn "straight, direct;" Danish igen "against;" Old Frisian jen, Old High German gegin, German gegen "against, toward," entgegen "against, in opposition to").

In Old English, eft (see eftsoons) was the main word for "again," but this often was strengthened by ongean, which became the principal word by 13c. Norse influence is responsible for the hard -g-. It was differentiated from against (q.v.) 16c. in southern writers, again becoming an adverb only, and against taking over as preposition and conjunction, but again clung to all senses in northern and Scottish dialect (where against was not adopted). Of action, "in return," early 13c.; of action or fact, "once more," late 14c.