interrex

From Latin inter- (“between”) + rex (“king”).

interrex (plural interrexes or interreges)

1. (historical) An official in Ancient Rome who acted as single head of state during the interregnum between two consulates.
2. (historical) An equivalent regent from the death of a Polish king till the election and enthronement of his successor.
3. (figuratively) A similar interim ruler, CEO, etc.

• interregnum
• rex sacrorum

From Latin inter- (“between”) + rex (“king”).

interrex m (plural interreges or interrexen, diminutive interrexje n)

1. (historical) An interrex, temporary head of state during the interregnum between two Roman consulates or from the death of a Polish king till the election and enthronement of his successor

From inter- +‎ rēx.

• (Classical) IPA^(key): /inˈter.reːks/, [ɪnˈtɛr.reːks]

interrēx m (genitive interrēgis); third declension

1. during the Roman Monarchy, the regent holding the royal power between the death of one king and the election of another
2. during the Roman Republic, one who who acted as head of state between two consulates

Third declension.

• interrex in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• interrex in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
• interrex in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition, 1883–1887)
• interrex in Harry Thurston Peck, editor (1898) Harper's Dictionary of Classical Antiquities, New York: Harper & Brothers
• interrex in William Smith et al., editor (1890) A Dictionary of Greek and Roman Antiquities, London: William Wayte. G. E. Marindin