The Collaborative International Dictionary of English v.0.48:

Comprehension \Com`pre*hen"sion\, n. [L. comprehensio: cf. F.
   compr['e]hension.]
   1. The act of comprehending, containing, or comprising;
      inclusion.
      [1913 Webster]

            In the Old Testament there is a close comprehension
            of the New; in the New, an open discovery of the
            Old.                                  --Hooker.
      [1913 Webster]

   2. That which is comprehended or inclosed within narrow
      limits; a summary; an epitome. [Obs.]
      [1913 Webster]

            Though not a catalogue of fundamentals, yet . . . a
            comprehension of them.                --Chillingworth.
      [1913 Webster]

   3. The capacity of the mind to perceive and understand; the
      power, act, or process of grasping with the intellect;
      perception; understanding; as, a comprehension of abstract
      principles.
      [1913 Webster]

   4. (Logic) The complement of attributes which make up the
      notion signified by a general term.
      [1913 Webster]

   5. (Rhet.) A figure by which the name of a whole is put for a
      part, or that of a part for a whole, or a definite number
      for an indefinite.
      [1913 Webster]

WordNet (r) 3.0 (2006):

comprehension
    n 1: an ability to understand the meaning or importance of
         something (or the knowledge acquired as a result); "how you
         can do that is beyond my comprehension"; "he was famous for
         his comprehension of American literature" [ant:
         incomprehension]
    2: the relation of comprising something; "he admired the
       inclusion of so many ideas in such a short work" [syn:
       inclusion, comprehension]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "comprehension":
   IQ, admissibility, admission, apprehension, assimilation, caliber,
   capacity, clairvoyance, command, completeness, comprehensiveness,
   comprisal, conception, conceptualization, coverage,
   deductive power, eligibility, embodiment, embracement,
   encompassment, envisagement, esemplastic power, exhaustiveness,
   foreknowledge, grasp, grip, ideation, inclusion, inclusiveness,
   incorporation, integrative power, intellect, intellection,
   intellectual grasp, intellectual power, intellectualism,
   intellectuality, intelligence, intelligence quotient, knowledge,
   mastery, membership, mental age, mental capacity, mental grasp,
   mental ratio, mentality, mother wit, native wit, openness,
   participation, power of mind, precognition, prehension,
   rationality, reasoning power, reception, sanity, savvy,
   scope of mind, sense, thinking power, tolerance, toleration,
   understanding, whole, wisdom, wit