I. e. the sender of rain, a surname of Jupiter among the Romans, to whom sacrifices were offered during long protracted droughts. These sacrifices were called aquilicium, "the calling forth of water," because certain magic ceremonies were performed by Etruscans to call down rain from heaven. (Tibull. i. 8. 26; Tertull. Apolog. 40; Fest. p. 2, ed. Mütller.)From Smith's Dictionary of Greek and Roman Biography and Mythology
From Ten Great Religions, by James Freeman Clarke
JUPITER, the chief god of Rome, according to most philologists, derives his name (like the Greek Ζεὸς) from the far-away Sanskrit word "Div" or "Diu," indicating the splendor of heaven or of day. Ju-piter is from "Djaus-Pitar," which is the Sanskrit for Father of Heaven, or else from "Diu-pitar," Father of Light. He is, at all events, the equivalent of the Olympian Zeus. He carries the lightning, and, under many appellations, is the supreme god of the skies. Many temples were erected to him in Rome, under various designations. He was called Pluvius, Fulgurator, Tonans, Fulminator, Imbricitor, Serenator,—from the substantives designating rain, lightning, thunder, and the serene sky. Anything struck with lightning became sacred, and was consecrated to Jupiter. As the supreme being he was called Optimus Maximus, also Imperator, Victor, Invictus, Stator, Prædator, Triumphator, and Urbis Custos. And temples or shrines were erected to him under all these names, as the head of the armies, and commander-in-chief of the legions; as Conqueror, as Invincible, as the Turner of Flight, as the God of Booty, and as the Guardian of the City. There is said to have been in Rome three hundred Jupiters, which must mean that Jupiter was worshipped under three hundred different attributes. Another name of this god was Elicius, from the belief that a method existed of eliciting or drawing down the lightning; which belief probably arose from an accidental anticipation of Dr. Franklin's famous experiment. There were no such myths told about Jupiter as concerning the Greek Zeus. The Latin deity was a much more solemn person, his whole time occupied with the care of the city and state. But traces of his origin as a ruler of the atmosphere remained rooted in language; and the Romans, in the time of Augustus, spoke familiarly of "a cold Jupiter," for a cold sky, and of a "bad Jupiter," for stormy weather.