The Collaborative International Dictionary of English v.0.48:

Plebeian \Ple*be"ian\, n.
   1. One of the plebs, or common people of ancient Rome, in
      distinction from patrician.
      [1913 Webster]

   2. One of the common people, or lower rank of men.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plebeian \Ple*be"ian\ (pl[-e]*b[=e]"yan), a. [L. plebeius, from
   plebs, plebis, the common people: cf. F. pl['e]b['e]ien.]
   1. Of or pertaining to the Roman plebs, or common people.
      [1913 Webster]

   2. Of or pertaining to the common people; vulgar; common; as,
      plebeian sports; a plebeian throng.
      [1913 Webster]

WordNet (r) 3.0 (2006):

plebeian
    adj 1: of or associated with the great masses of people; "the
           common people in those days suffered greatly"; "behavior
           that branded him as common"; "his square plebeian nose";
           "a vulgar and objectionable person"; "the unwashed
           masses" [syn: common, plebeian, vulgar, unwashed]
    n 1: one of the common people [syn: plebeian, pleb]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "plebeian":
   Babbittish, Cockney, Everyman, John Smith, Philistine, average man,
   base, baseborn, below the salt, bourgeois, brutish, campy, coarse,
   cockney, common, common man, commoner, commonplace, crass, gauche,
   general, high-camp, homely, homespun, humble, ignoble, inferior,
   kitschy, little fellow, little man, low, low-camp, low-class,
   lowborn, lowbred, lowbrow, lowly, mean, nonclerical, ordinary,
   plain, pleb, pop, popular, proletarian, provincial, public,
   roturier, rude, rustic, shabby-genteel, third-estate, uncouth,
   undistinguished, ungenteel, unpolished, unrefined, unwashed,
   vernacular, vulgar, working-class



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

PLEBEIAN. One who is classed among the common people, as distinguished from
the nobles. Happily in this country the order of nobles does not exist.



The Devil's Dictionary (1881-1906):

PLEBEIAN, n.  An ancient Roman who in the blood of his country stained
nothing but his hands.  Distinguished from the Patrician, who was a
saturated solution.