Consuetude

from WordNet (r) 3.0 (2006)

consuetude
    n 1: a custom or usage that has acquired the force of law

from The Collaborative International Dictionary of English v.0.48

Consuetude \Con"sue*tude\ (?; 144), n. [L. consuetudo. See
   {Custom}.]
   Custom, habit; usage. [R.]
   [1913 Webster]

         To observe this consuetude or law.       --Barnes
   .
   [1913 Webster]