Sunday (IPAEng: ˈ ˈsʌndi or sʌndeɪ, Listen) is the day of the week between Saturday and Monday. Sunday is traditionally associated with church attendance. In the Jewish law, Sunday is the first day of the Hebrew calendar week. In most Christian traditions it is considered the "Christian Sabbath", which is a change from seventh-day Sabbath or Jewish Shabbat. For many Christians it began to take the place of Shabbat as the day set apart for the public and solemn worship of God.

Sunday is considered the first day of the week in some countries, including the United States and Japan, although today many countries such as the United Kingdom regard Sunday as the seventh day, at least in the working week and the civil week.

Sunday is considered a non-working day in many countries of the world, and is part of "the weekend". Countries predominantly influenced by Jewish or Islamic religions have Friday or Saturday as a weekly non-working day instead.

The Gregorian calendar repeats every 400 years, and no century starts on a Sunday. The Jewish New Year never falls on a Sunday. Only those months beginning on a Sunday will contain a Friday the 13th.

Etymology

thumb|A depiction of Máni, the personified moon, and his sister Sól, the personified sun, from Norse mythology (1895) by Lorenz Frølich. The English noun Sunday derived sometime before 1250 from sunedai, which itself developed from Old English (before 700) Sunnandæg (literally meaning "day of the sun"), 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 søndag, and Swedish söndag). The Germanic term is a Germanic interpretation of Latin dies solis ("day of the sun"), which is a translation of the Greek heméra helíou.Barnhart (1995:778).

In most of the Indian Languages, the word for Sunday is Ravivar, Adivar and It'var, with Adi (Ah'-Dee) or Ravi being the Sanskrit names for the Sun.

The first Christian reference to Sunday is found in the First Apology of St. Justin Martyr (c. 150 AD). In a well-known passage of the Apology (Chapter 67), Justin describes the Christian custom of gathering for worship on Sunday. "And on the day called Sunday τοῦ ῾Ηλίου λεγομένη ἡμέρᾳ, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits . . .", he writes. Evidently Justin used the term Sunday because he was writing to a non-Christian, pagan audience. In Justin's time, Christians usually called Sunday the Lord's Day because they observed it as a weekly memorial of Jesus Christ's resurrection. The Roman Catholic Church believes that the resurrection of Christ occurred on the day following seventh-day Sabbath, which is Sunday, and makes it a portal to timeless eternity that transcends the seven-day weekly cycle.