“The term ‘patent’ is short for ‘letters patent,’ derived from the Latin literae patentes, meaning open letters. Generally, letters patent were letters addressed by the sovereign ‘to all whom these presents shall come,’ reciting a grant of some dignity, office, franchise, or other privilege that has been given by the sovereign to the patentee.” Donald S. Chisum et al., Principles of Patent Law 2 (1998).
literae patentes
literae patentes (lit-[schwa]r-ee p[schwa]-ten-teez), n. [Latin “open letters”] Hist. A public grant from the sovereign to a subject, conferring the right to land, a franchise, a title, liberty, or some other endowment. • The modern “patent” and, more closely, “letters patent” derive from this term. See LETTERS PATENT(1).