What's the "een" in Halloween?
"agreement between church and state on a mutual matter," 1610s, from French concordat (16c.), from Medieval Latin concordatum, noun use of Latin concordatum, neuter past participle of concordare "to agree," from concors (genitive concordis) "of one mind" (see concord).
a pact, with the force of international law, concluded between the ecclesiastical authority and the secular authority on matters of mutual concern; most especially a pact between the pope, as head of the Roman Catholic church, and a temporal head of state for the regulation of ecclesiastical affairs in the territory of the latter. Matters often dealt with in concordats include: the rights and liberties of the church; the creation and suppression of dioceses and parishes; the appointment of bishops, pastors, and military chaplains, sometimes with provision for their support; ecclesiastical immunities (e.g., exemption from military service); church property; questions relating to marriage; and religious education.