letters patent

From letters patents (archaic), from Late Middle English lettres patentes, lettres patent (“document or documents granting a privilege, power, or right, making an appointment or decree, etc.”) [and other forms], from Anglo-Norman lettres patentes (the plural of lettre patente), from Latin litterae patentēs, the plural of littera patēns (so called because they were written on open sheets of parchment), from littera (“letter”) + patēns (“accessible, open”) (the present active participle of pateō (“to be accessible or open; to be clear or evident”), from Proto-Indo-European *peth₂- (“to spread out; to fly”)). The English term is analysable as letters +‎ patent (“open, unconcealed; (archaic) open to public perusal”).