soon (adv.)

late Old English anon "straightway, forthwith," earlier on an, literally "into one," thus "continuously; straightway (in one course), at once;" see one. As a reply, "at once, coming!" By gradual misuse, "soon, in a little while" (1520s). An etymological one-word lesson in procrastination.

c. 1400, "precisely, exactly;" late 15c., "fittingly, snugly;" c. 1500, "immediately;" from just (adj.) and paralleling the adverbial use of French juste (also compare Dutch juist, German just, from the adjectives).

The original sense of "exactly" in space, time, kind, or degree; "precisely, without interval, deviation, or variation" is preserved in just so"exactly that, in that very way" (1751), just as I thought, etc. But the sense decayed, as it often does in general words for exactness (compare anon, soon), from "exactly, precisely, punctually" to "within a little; with very little but a sufficient difference; nearly; almost exactly;" then by 1660s to "merely, barely, by or within a narrow margin (as in just missed). Hence just now as "a short time ago" (1680s). Also "very lately, within a brief period of time" (18c.). It is also used intensively, "quite" (by 1855).

Just-so story is attested 1902 in Kipling, from just so "exactly that, in that very way."

obsolete or archaic way of saying "soon afterward," from Old English eftsona "a second time, repeatedly, soon after, again," from eft "afterward, again, a second time" (from Proto-Germanic *aftiz, from PIE root *apo- "off, away") + sona "immediately" (see soon). With adverbial genitive. Not in living use since 17c.