Wiktionary
n. (context legal English) a decree issued on a first petition for divorce; it becomes absolute at some later date unless cause is shown why it should not
WordNet
n. a decree issued on a first petition for divorce; becomes absolute at some later date
Wikipedia
A decree nisi or rule nisi is a court order that does not have any force unless a particular condition is met. Once the condition is met, the ruling becomes a decree absolute (rule absolute), and is binding. Typically, the condition is that an adversely affected party fail to provide satisfactory evidence or argument that the decree should not take effect (i.e. the decree takes effect unless the party shows that it shouldn't). For that reason, a decree nisi may also be called a rule, order or decree to show cause.
Using the example of a divorce, the wording of such a decree is generally in the form of "that the marriage, had and solemnized on (date) between AB and CD, be dissolved by reason that (grounds) UNLESS sufficient cause be shown to the court why this decree should not be made absolute within six weeks of the making hereof". This allows time for any party who objects to the divorce to come forward with those objections.
The term is used in many common law jurisdictions, but is more common in Britain than in the United States.
Usage examples of "decree nisi".
She started divorce proceedings against me and early in 1951 was granted her decree nisi.
I do not think I shall be violating the secrets of the confessional if I tell you that not many weeks ago, Sir Eustace came to me and formally asked me to sanction an engagement between them as soon as his wife's decree nisi had been pronounced.
It informed me that my wife had been awarded a decree nisi in the Divorce Court on the grounds of desertion, that she had decided to waive her right to any maintenance and that a sum of two thousand, three hundred and seventy-five pounds, my share of the proceeds of the sale of a flat in the Cromwell Road, jointly owned, had been credited to my account in the City Branch of the Great Western Bank.
In 1947 Robert was divorced from his wife, and when he received his decree nisi, he married me.