The Collaborative International Dictionary of English v.0.48:

Ritual \Rit"u*al\, a.[L. ritualis, fr. ritus a rite: cf. F.
   rituel.]
   Of or pertaining to rites or ritual; as, ritual service or
   sacrifices; the ritual law.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ritual \Rit"u*al\, n. [Cf. F. rituel.]
   1. A prescribed form of performing divine service in a
      particular church or communion; as, the Jewish ritual.
      [1913 Webster]

   2. Hence, the code of ceremonies observed by an organization;
      as, the ritual of the freemasons.
      [1913 Webster]

   3. A book containing the rites to be observed.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ritual
    adj 1: of or relating to or characteristic of religious rituals;
           "ritual killing"
    2: of or relating to or employed in social rites or rituals; "a
       ritual dance of Haiti"; "sedate little colonial tribe with
       its ritual tea parties"- Nadine Gordimer
    n 1: any customary observance or practice [syn: ritual,
         rite]
    2: the prescribed procedure for conducting religious ceremonies
    3: stereotyped behavior

Moby Thesaurus II by Grady Ward, 1.0:

148 Moby Thesaurus words for "ritual":
   High-Church, Sefer Torah, Torah, Torah scroll, Virginal, amenities,
   automatic, baccalaureate service, baptismal, bon ton, breviary,
   buckram, canon, celebration, ceremonial, ceremonies, ceremonious,
   ceremoniousness, ceremony, church book, civilities, commencement,
   conformity, consuetude, convention, conventional, convocation,
   custom, customary, decorous, dignities, dignity, duty, elegancies,
   empty formality, established way, etiquette, eucharistic,
   euchologion, euchology, exercise, exercises, extrinsicality, farse,
   fashion, folkway, form, form of worship, formal, formalities,
   formality, formalization, formula, formular, formulary, function,
   gentilities, graces, graduation, graduation exercises, gravity,
   habitual, hieratic, holy rite, impersonality, inaugural,
   inauguration, initiation, institution, lectionary, litany,
   liturgic, liturgistic, liturgy, machzor, manner, manners, manual,
   missal, mode of worship, mores, mummery, mystery, observance,
   office, order of worship, ordinal, ordinance, paschal, performance,
   perfunctory, pomp, pomposity, pompous, pontifical, practice,
   praxis, prayer book, prescribed, prescribed form, prescription,
   primness, procedural, proper thing, protocol, religious ceremony,
   rigidness, rite, rite de passage, rite of passage, rites,
   ritual observance, rituale, ritualistic, rituality, rituals,
   routine, rubric, sacerdotal, sacrament, sacramental,
   sacramentarian, service, service book, siddur, social convention,
   solemn, solemnity, solemnization, standard behavior,
   standard usage, standing custom, starchiness, stately, stiffness,
   stiltedness, stylization, time-honored practice, tradition, usage,
   use, usual, way, weight, well-mannered, what is done, wont,
   wonting