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]