The Collaborative International Dictionary
Ne Temere \Ne Te"me*re\ [So named from L. ne not + temere rashly, the first two words in the decree.] (R. C. Ch.) A decree of the Congregation of the Council declaring invalid [so far as the laws of the Roman Catholic Church are concerned] any marriage of a Roman Catholic, or of a person who has ever been a Roman Catholic, if not contracted before a duty qualified priest (or the bishop of the diocese) and at least two witnesses. The decree was issued Aug. 2, 1907, and took effect on Easter Apr. 19, 1908. The decree by its terms does not affect mixed marriages (those between Roman Catholics and persons of another faith) in Germany.
Wikipedia
Ne Temere was a decree issued in 1907 by the Roman Catholic Congregation of the Council regulating the canon law of the Church regarding marriage for practising Catholics. It is named for its opening words, which literally mean "lest rashly" in Latin.