For most Christians, Sunday is observed as a day of worship and rest, holding it as the Lord's Day and the day of Christ's resurrection. In some Muslim countries and Israel, Sunday is the first work day of the week. According to the Hebrew calendars and traditional Christian calendars, Sunday is the first day of the week. However, according to the International Organization for Standardization ISO 8601, Sunday is the seventh and last day of the week.
Sunday, being the day of the Sun, as the name of the first day of the week, is derived from Hellenistic astrology, where the seven planets, known in English as Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon, each had an hour of the day assigned to them, and the planet which was regent during the first hour of any day of the week gave its name to that day. During the 1st and 2nd century, the week of seven days was introduced into Rome from Egypt, and the Roman names of the planets were given to each successive day.
Germanic peoples seem to have adopted the week as a division of time from the Romans, but they changed the Roman names into those of corresponding Teutonic deities. Hence, the dies Solis became Sunday (German, Sonntag).
The English noun Sunday derived sometime before 1250 from sunedai, which itself developed from Old English (before 700) Sunnandg (literally meaning "sun's day"), which is cognate to other Germanic languages, including Old Frisian sunnandei, Old Saxon sunnundag, Middle Dutch sonnendach (modern Dutch zondag), Old High German sunnun tag (modern German Sonntag), and Old Norse sunnudagr (Danish and Norwegian sndag, Icelandic sunnudagur and Swedish sndag). The Germanic term is a Germanic interpretation of Latin dies solis ("day of the sun"), which is a translation of the Ancient Greek hemra helou. The p-Celtic Welsh language also translates the Latin "day of the sun" as dydd Sul.
In most Indian languages, the word for Sunday is Ravivra or Adityavra or its derived forms vra meaning day, Aditya and Ravi both being a style (manner of address) for Surya, the chief solar deity and one of the Adityas. Ravivra is first day cited in Jyotish, which provides logical reason for giving the name of each week day. In the Thai solar calendar of Thailand, the name ("Waan Arthit") is derived from Aditya, and the associated color is red.
In Russian the word for Sunday is (Voskreseniye) meaning "Resurrection". In other Slavic languages the word means "no work", for example Polish: Niedziela, Ukrainian: i, Belorussian: , Croatian: nedjelja, Serbian and Slovenian: Nedelja, Czech: Nedle, and Bulgarian: .
The Modern Greek word for Sunday, Greek: , is derived from Greek: (Kyrios, Lord) also, due to its liturgical significance as the day commemorating the resurrection of Jesus Christ, i.e. The Lord's Day.