"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 by 1903.