The Collaborative International Dictionary of English v.0.48:

Plebs \Plebs\ (pl[e^]bz), n. [L. Cf. Plebe.]
   1. The commonalty of ancient Rome who were citizens without
      the usual political rights; the plebeians; --
      distinguished from the patricians.
      [Webster 1913 Suppl.]

   2. Hence, the common people; the populace; -- construed as a
      pl.
      [Webster 1913 Suppl.]