The English noun Sunday derived sometime before 1250 from sunedai, which itself developed from Old English (before 700) Sunnandæg

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.

In most of the Indian Languages, the word for Sunday is or 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 [τῇ 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 the seventh-day Sabbath, which is Sunday, and makes it a portal to timeless eternity that transcends the seven-day weekly cycle.


Position in the week
The official ISO 8601 Calendar Standard states that Monday is the first day of the week. In the Judaeo-Christian tradition Sunday has been considered as the first day of the week. However, in most countries calendars show Monday as day 1 of the week. There are also countries where both types of calendar can be found, which causes trouble for over-enthusiastic computer software that attempts to dictate a user's calendrical preferences based purely on his location.

A number of languages appear to reflect Sunday's status as the first day of the week. In Greek, the names of the days Monday, Tuesday, Wednesday, and Thursday (Δευτέρα, Τρίτη, Τετάρτη, and Πέμπτη) mean "second", "third", "fourth", and "fifth", respectively. This suggests that Sunday was once counted as Πρώτη, that is, "first". The current Greek name for Sunday, Κυριακή, means "Lord's Day". A similar system of naming days of the week occurs in Portuguese. Monday is segunda-feira, which means "second day", also showing Sunday (domingo) to be counted as the first day. Similarly modern Latin uses "feria secunda" for Monday.

Slavonic languages use day-numbers that implicitly number Monday as 1, not 2. For example, Polish has czwartek (4) for Thursday and piątek (5) for Friday. [Hungarian péntek (Friday) is a cognate of this, although, Hungarian not being a Slavonic or even Indo-European language, the correlation with "5" is not evident to a Hungarian speaker].