The Collaborative International Dictionary of English v.0.48:

Psephism \Pse"phism\, n. [Gr. ? a decree, fr. ? to vote with a
   pebble, fr. ? pebble.] (Gr. Antiq.)
   A proposition adopted by a majority of votes; especially, one
   adopted by vote of the Athenian people; a statute. --J. P.
   Mahaffy.
   [1913 Webster]