The Collaborative International Dictionary of English v.0.48:

Dominical \Do*min"ic*al\, a. [LL. dominicalis, for L. dominicus
   belonging to a master or lord (dominica dies the Lord's day),
   fr. dominus master or lord: cf. F. dominical. See Dame.]
   1. Indicating, or pertaining to, the Lord's day, or Sunday.
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   2. Relating to, or given by, our Lord; as, the dominical (or
      Lord's) prayer. --Howell.
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            Some words altered in the dominical Gospels.
                                                  --Fuller.
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   Dominical altar (Eccl.), the high altar.

   Dominical letter, the letter which, in almanacs, denotes
      Sunday, or the Lord's day (dies Domini). The first seven
      letters of the alphabet are used for this purpose, the
      same letter standing for Sunday during a whole year
      (except in leap year, when the letter is changed at the
      end of February). After twenty-eight years the same
      letters return in the same order. The dominical letters go
      backwards one day every common year, and two every leap
      year; e. g., if the dominical letter of a common year be
      G, F will be the dominical letter for the next year.
      Called also Sunday letter. Cf. Solar cycle, under
      Cycle, n.
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