This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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adj. Law Taking effect at a specified date unless cause is shown for modification or nullification: a decree nisi.

conjunction. Unless; if not; -- used mostly in law.

Unless.

adj. not final or absolute

"_Peragere_ refers to the prosecution of a defendant carried to its end, but does not imply success for the prosecutor: see Pliny _Ep_ III ix 30 and Ulpian _Dig_ XLVIII v 2 1 'non alias ad mulierem possit peruenire, nisi reum peregerit [_sc_ adulterii]; peregisse autem non alias quis uidetur, _nisi et condemnauerit_'."

inconclusive   

decree nisi   

unless   

quidem    quod    neque    quae    ITA    nihil    aut    cum    nec    tibi