The Collaborative International Dictionary of English v.0.48:

Classification \Clas`si*fi*ca"tion\, n. [Cf. F. classification.]
   The act of forming into a class or classes; a distribution
   into groups, as classes, orders, families, etc., according to
   some common relations or affinities.
   [1913 Webster]

   Artificial classification. (Science) See under
      Artifitial.
      [1913 Webster]

WordNet (r) 3.0 (2006):

classification
    n 1: the act of distributing things into classes or categories
         of the same type [syn: categorization, categorisation,
         classification, compartmentalization,
         compartmentalisation, assortment]
    2: a group of people or things arranged by class or category
       [syn: classification, categorization, categorisation]
    3: the basic cognitive process of arranging into classes or
       categories [syn: classification, categorization,
       categorisation, sorting]
    4: restriction imposed by the government on documents or weapons
       that are available only to certain authorized people [ant:
       declassification]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "classification":
   antonomasia, appraisal, assessment, binomial nomenclature,
   biosystematics, biosystematy, categorization, class, evaluation,
   factoring, family, gauging, genus, glossology, grouping,
   identification, kingdom, nomenclature, onomastics, onomatology,
   order, orismology, phylum, place-names, place-naming, polyonymy,
   sifting, sifting out, sorting, sorting out, species, systematics,
   taxonomy, terminology, toponymy, trinomialism, weighing,
   winnowing