"set number of persons, selected according to law and sworn to determine the facts and truth of a case or charge submitted to them and render a verdict," early 14c. (late 12c. in Anglo-Latin), from Anglo-French and Old French juree (13c.), from Medieval Latin iurata "an oath, a judicial inquest, sworn body of men," noun use of fem. past participle of Latin iurare "to swear," from ius (genitive iuris) "law, an oath" (see jurist).

Meaning "body of persons chosen to award prizes at an exhibition" is from 1851. Grand jury attested from early 15c. in Anglo-French (le graund Jurre), literally "large," so called with reference to the number of its members (usually 12 to 23). Jury-box is from 1729; juryman from 1570s. Figurative phrase jury is still out "no decision has been made" is from 1957.

"of a grammatical mode expressing command," 1825, with -ive + Latin iuss-, past participle stem of iubere "to bid, command, to order," from PIE root *ioudh- "to cause to move" (cognates: Sanskrit yudhya- "to fight," yodha- "to rebel;" Greek hysmine "battle, fight;" Lithuanian judėti "to move" (intransitive), judus "belligerent"). The sense evolution in Latin was from "cause to move" to "order." As a noun from 1836.

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."