Emily Dickinson Lexicon

SUN'DAY, n. [Sax: sunna-dæg; G. sonntag; D. zondag; Dan. söndag; Sw. söndag; so called because this day was anciently dedicated to the sun, or to its worship.]

The Christian sabbath; the first day of the week, a day consecrated to rest from secular employments, and to religious worship. It is called also the Lord's day. Many pious persons however discard the use of Sunday, and call the day the sabbath. [See Sabbath.]