The Collaborative International Dictionary of English v.0.48:

Eunomy \Eu"no*my\, n. [Gr. ?; e'y^ well + ? law.]
   Equal law, or a well-adjusted constitution of government.
   [R.] --Mitford.
   [1913 Webster]

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

EUNOMY. Equal laws, and a well adjusted constitution of government.