The Collaborative International Dictionary of English v.0.48:

Ceremonious \Cer`e*mo"ni*ous\, a. [Cf. F. c['e]r['e]monieux, L.
   Caerimoniosus.]
   1. Consisting of outward forms and rites; ceremonial.

   Note: [In this sense ceremonial is now preferred.]
         [1913 Webster]

               The ceremonious part of His worship. --South.
         [1913 Webster]

   2. According to prescribed or customary rules and forms;
      devoted to forms and ceremonies; formally respectful;
      punctilious. "Ceremonious phrases." --Addison.
      [1913 Webster]

            Too ceremonious and traditional.      --Shak.

   Syn: Formal; precise; exact. See Formal.
        [1913 Webster]

WordNet (r) 3.0 (2006):

ceremonious
    adj 1: characterized by pomp and ceremony and stately display
           [syn: pompous, ceremonious]
    2: rigidly formal or bound by convention; "their ceremonious
       greetings did not seem heartfelt" [syn: ceremonious,
       conventional]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "ceremonious":
   High-Church, attentive, baptismal, cap in hand, careful,
   ceremonial, chivalric, chivalrous, civil, conventional, correct,
   courteous, courtly, decorous, deferential, dignified, dutiful,
   eucharistic, formal, formular, formulary, gallant, grandiose,
   hieratic, honorific, imposing, impressive, knightly, liturgic,
   liturgistic, majestic, moving, old-fashioned, old-world, paschal,
   polite, pompous, proper, punctilious, regardful, respectful,
   ritual, ritualistic, sacerdotal, sacramental, sacramentarian,
   seemly, solemn, starchy, stately, stiff, striking, stuffy,
   well-mannered