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):

encyclopaedia
    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]