From Latin 'jocus' (game), via Medieval Latin 'jocale' (plaything) — a jewel was a trifle to play with.
A precious stone; a personal ornament containing gems.
From Old French 'jouel' (ornament), possibly from Medieval Latin 'jocale' (plaything), from Latin 'jocus' (game, jest). A jewel was originally a plaything. Key roots: jocus (Latin: "game, jest").