Jupiter (n.) Look up Jupiter at Dictionary.com
c.1200, "supreme deity of the ancient Romans," from Latin Iupeter, from PIE *dyeu-peter- "god-father" (originally vocative, "the name naturally occurring most frequently in invocations" [Tucker]), from *deiw-os "god" (see Zeus) + peter "father" in the sense of "male head of a household" (see father). Compare Greek Zeu pater, vocative of Zeus pater "Father Zeus;" Sanskrit Dyauspita "heavenly father." The planet name is attested from late 13c. Jupiter Pluvius "Jupiter as dispenser of rain" was used jocularly from 1864.