ius iurandum

Latin

From iūs (“law”) +‎ iūrandus (“vowed”).

(Classical Latin) IPA^(key): /i̯uːs i̯uːˈran.dum/, [i̯uːs̠ i̯uːˈrän̪d̪ʊ̃ˑ]
(modern Italianate Ecclesiastical) IPA^(key): /jus juˈran.dum/, [jus juˈrän̪d̪um]

iūs iūrandum n (genitive iūris iūrandī); third declension

an oath
Synonyms: iūrāmentum, iūrandum
- c. 52 BCE, Julius Caesar, Commentarii de Bello Gallico 1.3:
  Hac oratione adducti inter se fidem et ius iurandum dant et regno occupato per tres potentissimos ac firmissimos populos totius Galliae sese potiri posse sperant.
  Incited by this speech, they give a pledge and oath to one another, and hope that, when they have seized the sovereignty, they will, by means of the three most powerful and valiant nations, be enabled to obtain possession of the whole of Gaul.

Third-declension noun (neuter, imparisyllabic non-i-stem) with a second-declension adjective.