Lewis & Short

dējĕro, āvi, ātum (the later form de-jūro, found in many edd., is now retained only in Gell. 1, 3, 20; 11, 6, 1), 1, v. n. [dejuro, with shortened rad. vowel; cf. Corss. Ausspr. 2, 203], to take an oath, to swear (ante- and post-class.): per omnes deos et deas dejeravit, Plaut. Cas. 3, 5, 37; id. Rud. 5, 2, 40; Ter. Eun. 2, 3, 39; id. Hec. 5, 2, 5; Varr. L. L. 5, § 6 Müll.: cum ille dejerasset, Gell. 4, 20, 9 al; Vulg. 1 Reg. 20, 17; id. Eccl. 9, 2. (In Prop. 4 (5), 3, 42, the true reading is pejerat.)