The Collaborative International Dictionary of English v.0.48:

Analogy \A*nal"o*gy\, n.; pl. Analogies. [L. analogia, Gr. ?,
   fr. ?: cf. F. analogie. See Analogous.]
   1. A resemblance of relations; an agreement or likeness
      between things in some circumstances or effects, when the
      things are otherwise entirely different. Thus, learning
      enlightens the mind, because it is to the mind what light
      is to the eye, enabling it to discover things before
      hidden.
      [1913 Webster]

   Note: Followed by between, to, or with; as, there is an
         analogy between these objects, or one thing has an
         analogy to or with another.
         [1913 Webster]

   Note: Analogy is very commonly used to denote similarity or
         essential resemblance; but its specific meaning is a
         similarity of relations, and in this consists the
         difference between the argument from example and that
         from analogy. In the former, we argue from the mere
         similarity of two things; in the latter, from the
         similarity of their relations. --Karslake.
         [1913 Webster]

   2. (Biol.) A relation or correspondence in function, between
      organs or parts which are decidedly different.
      [1913 Webster]

   3. (Geom.) Proportion; equality of ratios.
      [1913 Webster]

   4. (Gram.) Conformity of words to the genius, structure, or
      general rules of a language; similarity of origin,
      inflection, or principle of pronunciation, and the like,
      as opposed to anomaly. --Johnson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

analogy
    n 1: an inference that if things agree in some respects they
         probably agree in others
    2: drawing a comparison in order to show a similarity in some
       respect; "the operation of a computer presents and
       interesting analogy to the working of the brain"; "the models
       show by analogy how matter is built up"
    3: the religious belief that between creature and creator no
       similarity can be found so great but that the dissimilarity
       is always greater; any analogy between God and humans will
       always be inadequate [syn: doctrine of analogy, analogy]
       [ant: apophatism, cataphatism]

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "analogy":
   accordance, affinity, agent, agreement, alignment, alikeness,
   allegory, alliance, alternate, alternative, ambiguity, aping,
   approach, approximation, assimilation, backup, balancing, change,
   changeling, closeness, coextension, collineation, community,
   comparability, comparative anatomy, comparative degree,
   comparative grammar, comparative judgment, comparative linguistics,
   comparative literature, comparative method, compare, comparing,
   comparison, concurrence, conformity, confrontation, confrontment,
   contrast, contrastiveness, copy, copying, correlation,
   correspondence, counterfeit, deputy, distinction, distinctiveness,
   double, dummy, equal, equidistance, equivalent, equivocation,
   equivoque, ersatz, exchange, fake, fill-in, ghost, ghostwriter,
   identity, imitation, likeness, likening, locum tenens, makeshift,
   matching, metaphor, metonymy, mimicking, nearness, next best thing,
   nondivergence, opposing, opposition, parallelism, parity,
   personnel, phony, pinch hitter, proportion, proxy, relation,
   relief, replacement, representative, resemblance, reserves, ringer,
   sameness, second string, secondary, semblance, sign, similarity,
   simile, similitude, simulation, spares, stand-in, sub, substituent,
   substitute, substitution, succedaneum, superseder, supplanter,
   surrogate, symbol, synecdoche, tergiversation, third string, token,
   trope of comparison, understudy, utility player, vicar,
   vice-president, vice-regent, weighing



Bouvier's Law Dictionary, Revised 6th Ed (1856):

ANALOGY, construction. The similitude of relations which exist between things

compared.
     2. To reason analogically, is to draw conclusions based on this
similitude of relations, on the resemblance, or the connexion which is
perceived between the objects compared. "It is this guide," says Toollier,
which leads the law lawgiver, like other men, without his observing it. It
is analogy which induces us, with reason, to suppose that, following the
example of the Creator of the universe, the lawgiver has established general
and uniform laws, which it is unnecessary to repeat in all analogous cases."
Dr. Civ. Fr. liv. 3, t. 1, c. 1. Vide Ang. on Adv. Enjoym. 30, 31; Hale's
Com. Law, 141.
     3. Analogy has been declared to be an argument or guide in forming
legal judgments, and is very commonly a ground of such judgments. 7 Barn. &
Cres. 168; 3 Bing. R. 265; 8 Bing R. 557, 563; 3 Atk. 313; 1 Eden's R. 212;
1 W. Bl. 151; 6 Ves. jr. 675, 676; 3 Swanst. R. 561; 1 Turn. & R. 103, 338;
1 R. & M. 352, 475, 477; 4 Burr. R. 1962; 2022, 2068; 4 T. R. 591; 4 Barn. &
Cr. 855; 7 Dowl. & Ry. 251; Cas. t. Talb. 140; 3 P. Wms. 391; 3 Bro. C. C.
639, n.