The Collaborative International Dictionary of English v.0.48:

Encyclopedia \En*cy`clo*pe"di*a\, Encyclopaedia
\En*cy`clo*p[ae]"di*a\, n. [NL., fr. Gr. ?, for ? ?, instruction
   in the circle of arts and sciences: cf. F. encyclop['e]die.
   See Cyclopedia, and Encyclical.] [Formerly written
   encyclop[ae]dy and encyclopedy.]
   The full circle of arts and sciences; a comprehensive summary
   of knowledge, or of a branch of knowledge; esp., a work in
   which the various branches of science or art are discussed
   separately, and usually in alphabetical order; a cyclopedia.
   [1913 Webster]

WordNet (r) 3.0 (2006):

encyclopedia
    n 1: a reference work (often in several volumes) containing
         articles on various topics (often arranged in alphabetical
         order) dealing with the entire range of human knowledge or
         with some particular specialty [syn: encyclopedia,
         cyclopedia, encyclopaedia, cyclopaedia]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "encyclopedia":
   atlas, bibliography, body of knowledge, body of learning, calendar,
   casebook, catalog, catalogue raisonne, city directory,
   classified catalog, concordance, cyclopedia, diatesseron,
   dictionary catalog, directory, gazetteer, harmony, index,
   literature, lore, materials, phone book, polyglot, publications,
   record book, reference book, source book, store of knowledge,
   studbook, system of knowledge, telephone book, telephone directory,
   treasury of information, work of reference