The Collaborative International Dictionary of English v.0.48:

Shrove \Shrove\,
   imp. of Shrive.
   [1913 Webster]

   Shrove Sunday, Quinguagesima Sunday.

   Shrove Tuesday, the Tuesday following Quinguagesima Sunday,
      and preceding the first day of Lent, or Ash Wednesday.

   Note: It was formerly customary in England, on this day, for
         the people to confess their sins to their parish
         priests, after which they dined on pancakes, or
         fritters, and the occasion became one of merriment. The
         bell rung on this day is popularly called Pancake Bell,
         and the day itself Pancake Tuesday. --P. Cyc.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Shrove Tuesday
    n 1: the last day before Lent [syn: Mardi Gras, Shrove
         Tuesday, pancake day]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "Shrove Tuesday":
   Advent, Allhallowmas, Allhallows, Allhallowtide, Annunciation,
   Annunciation Day, Ascension Day, Ash Wednesday, Candlemas,
   Candlemas Day, Carnival, Christmas, Corpus Christi, Easter,
   Easter Monday, Easter Saturday, Easter Sunday, Eastertide,
   Ember days, Epiphany, Good Friday, Halloween, Hallowmas,
   Holy Thursday, Holy Week, Lady Day, Lammas, Lammas Day, Lammastide,
   Lent, Lententide, Mardi Gras, Martinmas, Maundy Thursday,
   Michaelmas, Michaelmas Day, Michaelmastide, Palm Sunday,
   Pancake Day, Passion Week, Pentecost, Quadragesima,
   Quadragesima Sunday, Septuagesima, Trinity Sunday, Twelfth-day,
   Twelfth-tide, Whit-Tuesday, White Sunday, Whitmonday, Whitsun,
   Whitsunday, Whitsuntide, Whitweek