The only free and comprehensive online etymological dictionary of the Spanish language
día m. (Noun) "day"
10th cent. From Vulgar Latin *dia, from Latin dies 'id.,' originally dius. From Proto-Italic *diē- 'id.' From Proto-Indo-European *di̯-eu̯-, the name of the Indo-European sky god. See also dios.
Indo-European
Romance
Asturian día, Portuguese dia, Galician día, Catalan dia, French -di, Italian , Aromanian dzuã, Romanian zi, Sardinian día
Italic
Oscan iúkleí "on the day" (< *di̯o-kelo-), Umbrian tiçel "day?" (meaning uncertain)
Celtic
Old Irish dïe, Old Welsh did, Old Breton ded, Old Cornish det
Balto-Slavic
Old Church Slavonic dьnь, Lithuanian dienà
Armenian
Armenian tiw
Indo-Iranian
Sanskrit dyáv- "day," "Sky Father," "god of the sky"