The Collaborative International Dictionary of English v.0.48:

Week \Week\, n. [OE. weke, wike, woke, wuke AS. weocu, wicu,
   wucu; akin to OS. wika, OFries. wike, D. week, G. woche, OHG.
   wohha, wehha, Icel. vika, Sw. vecka, Dan. uge, Goth. wik?,
   probably originally meaning, a succession or change, and akin
   to G. wechsel change, L. vicis turn, alternation, and E.
   weak. Cf. Weak.]
   A period of seven days, usually that reckoned from one
   Sabbath or Sunday to the next.
   [1913 Webster]

         I fast twice in the week.                --Luke xviii.
                                                  12.
   [1913 Webster]

   Note: Although it [the week] did not enter into the calendar
         of the Greeks, and was not introduced at Rome till
         after the reign of Theodesius, it has been employed
         from time immemorial in almost all Eastern countries.
         --Encyc. Brit.
         [1913 Webster]

   Feast of Weeks. See Pentecost, 1.

   Prophetic week, a week of years, or seven years. --Dan. ix.
      24.

   Week day. See under Day.
      [1913 Webster]

WordNet (r) 3.0 (2006):

week
    n 1: any period of seven consecutive days; "it rained for a
         week" [syn: week, hebdomad]
    2: hours or days of work in a calendar week; "they worked a
       40-hour week" [syn: workweek, week]
    3: a period of seven consecutive days starting on Sunday [syn:
       week, calendar week]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "week":
   Heptateuch, abundant year, academic year, annum, bissextile year,
   calendar month, calendar year, century, common year, day, decade,
   decennary, decennium, defective year, fiscal year, fortnight,
   heptachord, heptad, heptagon, heptahedron, heptameter, heptarchy,
   heptastich, hour, leap year, lunar month, lunar year, lunation,
   luster, lustrum, man-hour, microsecond, millennium, millisecond,
   minute, moment, month, moon, quarter, quinquennium, regular year,
   second, semester, septennate, septet, septuor, session, seven,
   sevener, sidereal year, solar year, sun, term, trimester,
   twelvemonth, weekday, year



Easton's 1897 Bible Dictionary:

Week
   From the beginning, time was divided into weeks, each consisting
   of six days of working and one of rest (Gen. 2:2, 3; 7:10; 8:10,
   12; 29:28). The references to this division of days becomes
   afterwards more frequent (Ex. 34:22; Lev. 12:5; Num. 28:26;
   Deut. 16:16; 2 Chr. 8:13; Jer. 5:24; Dan. 9:24-27; 10:2, 3). It
   has been found to exist among almost all nations.


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

WEEK. Seven days of time.
     2. The week commences immediately after twelve o'clock, on the night
between Saturday and Sunday, and ends at twelve o'clock, seven days of
twenty-four hours each thereafter.
     3. The first day of the week is called Sunday; (q.v.) the second,
Monday; the third, Tuesday; the, fourth, Wednesday; the fifth, Thursday; the
sixth, Friday; and the seventh, Saturday. Vide 4 Pet. S. C. Rep. 361.