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.