The Collaborative International Dictionary of English v.0.48:

Sunday \Sun"day\, n. [AS. sunnandaeg; sunne, gen. sunnan, the
   sun + daeg day; akin to D. zondag, G. sonntag; -- so called
   because this day was anciently dedicated to the sun, or to
   its worship. See Sun, and Day.]
   The first day of the week, -- consecrated among Christians to
   rest from secular employments, and to religious worship; the
   Christian Sabbath; the Lord's Day.
   [1913 Webster]

   Advent Sunday, Low Sunday, Passion Sunday, etc. See
      under Advent, Low, etc.
      [1913 Webster]

   Syn: See Sabbath.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sunday \Sun"day\, a.
   Belonging to the Christian Sabbath.
   [1913 Webster]

   Sunday letter. See Dominical letter, under Dominical.


   Sunday school. See under School.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Sunday
    n 1: first day of the week; observed as a day of rest and
         worship by most Christians [syn: Sunday, Lord's Day,
         Dominicus, Sun]
    2: United States evangelist (1862-1935) [syn: Sunday, Billy
       Sunday, William Ashley Sunday]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "Sunday":
   Christmas, First day, Sabbath, church calendar, day of rest,
   dies non, ecclesiastical calendar, fast, feast, go on furlough,
   go on leave, holiday, holy day, holytide, make holiday,
   take a holiday, take leave, vacation, weekend



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SUNDAY. The first day of the week.
     2. In some of the New England states it begins at sun setting on
Saturday, and ends at the same time the next day. But in other parts of the
United States, it generally commences at twelve o'clock on the night between
Saturday and Sunday, and ends in twenty-four hours thereafter. 6, Gill. &
John. 268; and vide Bac. Ab. Heresy, &c. D; Id. Sheriff, N 4; 1 Salk. 78; 1
Sell. Pr. 12; Hamm. N. P. 140. The Sabbath, the Lord's Day, and Sunday, all
mean the same thing. 6 Gill. & John. 268; see 6 Watts, 231; 3 Watts, 56, 59.
     2. In some states, owing to statutory provisions, contracts made on
Sunday are void; 6 Watts, R. 231; Leigh, N. P. 14; 1 P. A. Browne, 171; 5 B.
& C. 406; 4 Bing. 84; but in general they are binding, although made on that
day, if good in other respects. 1 Crompt. & Jervis, 130; 3 Law Intell. 210;
Chit. on Bills, 59; Wright's R. 764;,10 Mass. 312 1 Cowen, R. 76, n.; Cowp.
640; 1 Bl. Rep. 499; 1 Str. 702; see 8 Cowen, R. 27; 6 Penn. St. R. 417,
420.
     4. Sundays are computed in the time allowed for the performance of an
act, but if the last day happen to be a Sunday, it is to be excluded, and
the act must in general be performed on Saturday; 3 Penna. R. 201; 3 Chit.
Pr. 110; promissory notes and bills of exchange, when they fall due on
Sunday, are generally paid on Saturday. See, as to the origin of keeping
Sunday as a holiday, Neale's F. & F. Index, Lord's day; Story on Pr. Notes,
Sec. 220; Story on Bills, Sec. 233; 2 Hill's N. Y. Rep. 587; 2 Applet. R.
264.