[1] : The Collaborative International Dictionary of English v.0.48

middle \mid"dle\ mi^d"d'l, a. oe. middel, as. middel; akin
   to d. middel, ohg. muttil, g. mittel. root271. see mid,
   a.
   1913 webster
   1. equally distant from the extreme either of a number of
      things or of one thing; mean; medial; as, the middle house
      in a row; a middle rank or station in life; flowers of
      middle summer; men of middle age.
      1913 webster

   2. intermediate; intervening.
      1913 webster

            will, seeking good, finds many middle ends. --sir j.
                                                  davies.
      1913 webster

   note: middle is sometimes used in the formation of
         self-explaining compounds; as, middle-sized,
         middle-witted.
         1913 webster

   middle ages, the period of time intervening between the
      decline of the roman empire and the revival of letters.
      hallam regards it as beginning with the sixth and ending
      with the fifteenth century.

   middle class, in england, people who have an intermediate
      position between the aristocracy and the artisan class. it
      includes professional men, bankers, merchants, and small
      landed proprietors
      1913 webster

            the middle-class electorate of great britain. --m.
                                                  arnold.
      1913 webster

   middle distance. paint. see middle-ground.

   middle english. see english, n., 2.

   middle kingdom, china.

   middle oil chem., that part of the distillate obtained
      from coal tar which passes over between 170deg and
      230deg centigrade; -- distinguished from the light
      oil, and the heavy oil or dead oil.

   middle passage, in the slave trade, that part of the
      atlantic ocean between africa and the west indies.

   middle post. arch. same as king-post.

   middle states, new york, new jersey, pennsylvania, and
      delaware; which, at the time of the formation of the
      union, occupied a middle position between the eastern
      states or new england and the southern states. u.s.

   middle term logic, that term of a syllogism with which
      the two extremes are separately compared, and by means of
      which they are brought together in the conclusion.
      --brande.

   middle tint paint., a subdued or neutral tint.
      --fairholt.

   middle voice. gram. see under voice.

   middle watch, the period from midnight to four a. m.; also,
      the men on watch during that time. --ham. nav. encyc.

   middle weight, a pugilist, boxer, or wrestler classed as of
      medium weight, i. e., over 140 and not over 160 lbs., in
      distinction from those classed as light weights, heavy
      weights, etc.
      1913 webster
see also:
mid middle ages middle class middle distance middle-ground middle english 
english middle kingdom middle oil light oil heavy oil 
dead oil middle passage middle post king-post middle states 
middle term middle tint middle voice voice middle watch 
middle weight light weights heavy weights 

[2] : WordNet (r) 2.0

middle class
     n : the social class between the lower and upper classes syn: bourgeoisie
see also:
bourgeoisie 

[3] : Moby Thesaurus II by Grady Ward, 1.0

49 moby thesaurus words for "middle class":
   middle america, bourgeoisie, burgherdom, common people, common run,
   common sort, commonage, commonality, commonalty, commoners,
   commons, fourth-rater, laborers, linendrapers, lower classes,
   lower middle class, lower orders, lumpen proletariat, mediocrity,
   middle order, middle orders, no prize, nobody special, nonentity,
   nothing special, ordinary people, peasantry, plain folks,
   plain people, proletariat, rank and file, second-rater,
   shopkeepers, silent majority, small beer, small potatoes,
   small tradesmen, suburbia, the lower cut, the other half,
   the third estate, third-rater, tinhorn, toilers, toiling class,
   upper middle class, vulgus, working class, working people

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