According to Webster's Ninth New Collegiate Dictionary (1983), the term 'weekend', first recorded in 1878, refers to 'the period between the close of one working or business or school week and the beginning of the next'. This concept firmly places Sunday at the end of the week.

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That may be true, but the Sabbath was long established in the culture before this definition came about. How is it, then, that this definition would override that?

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Most along with myself disregarded that other crap and wanted a better system. The 5-2 week system was found to be very good and so it is used mostly.

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So, you're saying (I hope I'm assuming correctly) that the business-week forces the sabbath to be on a Sunday since it is more convenient for everyone?

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Yep

First Day Sabbath: Since Puritan times, most English-speaking Protestants equate "Lord's Day" (viz., Sunday) with "Sabbath", as do most Roman Catholic and some Eastern Orthodox faiths; kept in commemoration of the resurrection of Christ, it is often celebrated with the Eucharist. For many it is the day of rest, and of communal worship in remembrance of Resurrection Day. It is considered both the first day and the "eighth day" of the seven-day week (although Sunday is designated the "seventh" day of the week in the ISO 8601 standard). Relatively few Christians (as in the Church of Scotland) regard first-day observance as entailing all of the ordinances of Jewish Shabbat in a more rigorous abstention from "worldly" activities. The related Latter Day Saint movement generally follows the stronger of first-day Christian Sabbatarian traditions, avoiding shopping, leisure activities, and work unless absolutely necessary; and in Tonga, all commerce and entertainment activities cease from midnight Saturday until midnight Sunday, and its constitution declares this Sabbath sacred forever. Sometimes Lord's Day is observed by those who believe Sabbath corresponds to Saturday but is obsolete. In Oriental Orthodoxy, the Ethiopian Orthodox Tewahedo Church has observed both Sunday Resurrection Day and Saturday Sabbath in different ways for several centuries, as have other Eastern Orthodox traditions. As another minority view, some modern Christians uphold Sabbath principles but do not limit observance to either Saturday or Sunday, instead advocating rest on any one chosen day of the week, or advocating Sabbath as instead a symbolic metaphor for rest in Christ.

Seventh Day Sabbath: Several Christian denominations still observe Sabbath in a similar manner to Judaism, but observance ends at Saturday sunset instead of Saturday nightfall; church historians Sozomen and Socrates cite the seventh day as the Christian day of worship except for certain specified pagan-influenced cities. Many Sabbatarian Judeo-Christian groups were attested during the Middle Ages; the Szekler Sabbatarians were founded in 1588 from among the Unitarian Church of Transylvania and maintained a presence until the group was converted to Judaism in the 1870s. Seventh Day Baptists have observed Sabbath on Saturday since the mid-17th century (either from sundown or from midnight), and influenced the more numerous Seventh-day Adventists in America toward that doctrine in the mid-19th century. They and others believe that keeping seventh-day Sabbath is a moral responsibility equal to that of any of the Ten Commandments. They also use "Lord's Day" to mean the seventh day, based on Scriptures in which God calls the day "my Sabbath" (Exodus 31:13) and "to the Lord" (Exodus 16:23). The question of defining Sabbath worldwide on a round earth was resolved by some seventh-day Sabbatarians by making use of the International Date Line (i.e., permitting local rest-day adjustment, Esther 9:16-19), while others (such as some Alaskan Sabbatarians) keep Sabbath according to Jerusalem time (i.e., rejecting manmade temporal customs, Daniel 7:25). Many of the Lemba in southern Africa, like some other African tribes, are Christians and claim common descent from the Biblical Israelites, keep one day a week holy like Sabbath, and maintain many beliefs and practices associated with Judaism.