The Collaborative International Dictionary of English v.0.48:

Dies non \Di"es non"\ [L. dies non juridicus.] (Law)
   A day on which courts are not held, as Sunday or any legal
   holiday.
   [1913 Webster]

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

DIES NON or DIES NON JURIDICI. Non-judicial days. Days during which courts
do not transact any business, as Sunday. The entry of judgment upon such a
day is void. W. Jones, 156.