custos regni

Meaning

Noun

• A kind of viceregal locum tenens appointed, either alone or jointly, to execute the political duties of a monarch during his or her absence from the seat of government.

Origin

• First attested in the plural in October 1644 and in the singular in 1683; Latin: custōs + rēgnī (“of royal power”; genitive singular of rēgnum, “royal power”, “kingdom”) = “custodian of royal power” ≈ “guardian of the realm”.