Mid 19th century. From classical Latin pacta, plural of pactum + sunt servanda ‘(they) must be kept’, after pacta et promissa semperne servanda sint whether agreements and promises should always be kept (Cicero De Officiis 3. 92); compare ideo servandum erit pactum conventum thus it will be necessary to keep the agreement made (Justinian Digest 2. 14. 13. 1).