Jupiter (mythology) practice of swearing by Jove to witness an oath in law courts is the origin of the expression "by Jove!"—archaic, but still in use. The name of the god was also adopted as the name of the planet Jupiter; the adjective "jovial" originally described those born under the planet of Jupiter (reputed to be jolly, optimistic, and buoyant in temperament). Jove was the original namesake of Latin forms of the weekday now known in English as Thursday (originally called "Iovis Dies" in Latin). These became "jeudi" in French, "jueves" in Spanish, "joi" in Romanian, "giovedì" in Italian, "dijous" in Catalan,
Godefroy Wendelin illud sensus testatur, plane ut est cum sex planetis circa Solem, sic etiam se rem habere cum quatuor Jovialibus, ut circa corpus Jovis quilibet, quo longius ab illo potest excurrere, hoc tardius redeat, et id quidem proportione non eadem, sed majore, hoc est sescupla proportionis intervallorum cujusque a Jove: quae plane ipsissima est, qua utebantur supra sex planetae. Intervalla enim quatuor Jovialium a Jove prodit Marius in suo Mundo Joviali ista: 3, 5, 8, 13 (vel 14 Galilaeo) … Periodica vero tempora prodit idem Marius ista: dies 1. h. 18 1/2, dies 3 h. 13 1/3, dies 7 h. 3,