The Collaborative International Dictionary of English v.0.48:

Banns \Banns\ (b[a^]nz), n. pl. [See Ban.]
   Notice of a proposed marriage, proclaimed in a church, or
   other place prescribed by law, in order that any person may
   object, if he knows of just cause why the marriage should not
   take place.
   [1913 Webster]

WordNet (r) 3.0 (2006):

banns
    n 1: a public announcement of a proposed marriage