The Collaborative International Dictionary of English v.0.48:

Oyez \O"yez`\ ([=o]"y[e^]s`; 277), interj. [Anglo-F. oyez hear
   ye. See Oyer.]
   Hear; attend; -- a term used by criers of courts to secure
   silence before making a proclamation. It is repeated three
   times. [Written also oyes.]
   [1913 Webster]