Etymology
1. 1376, "open letter or document from some authority," shortened form of Anglo-Fr.
lettre patent (also in M.L.
(litteræ) patentes), lit. "open letter" (1292), from O.Fr.
patente (adj.), from L.
patentum (nom.
patens) "open, lying open," prp. of
patere "lie open, be open," from PIE
*pet- "to spread" (cf. Gk.
petannynai "to spread out,"
petalon "leaf," O.N.
faðmr "embrace, bosom," O.E.
fæðm "embrace, fathom").
"The Letters Patent were ... written upon open sheets of parchment, with the Great Seal pendent at the bottom ... [while] the 'Litteræ Clausæ,' or Letters Close, ... being of a more private nature, and addressed to one or two individuals only, were closed or folded up and sealed on the outside." [S.R. Scargill-Bird, "A Guide to the Principal Classes of Documents at the Public Record Office," 1891]
The adj. sense of "open to view, plain, clear" is first recorded 1508; the verb "to obtain right to land" is attested from 1675. The meaning "copyright an invention" is first recorded 1822, from earlier meaning "obtain exclusive right or monopoly" (1789), a privilege granted by the Crown via letters patent.
2. The noun is derived from Middle English patent (“document granting an office, property, right, title, etc.; document granting permission, licence; papal indulgence, pardon”) [and other forms], which is either:
3. * a clipping of lettre patent, lettres patente, lettres patentes [and other forms]; or
4. * directly from Anglo-Norman and Middle French patente (modern French patent), a clipping of Anglo-Norman lettres patentes, Middle French lettres patentes, lettre patente, and Old French patentes lettres (“document granting an office, privilege, right, etc., or making a decree”) (compare Late Latin patēns, littera patēns, litterae patentēs).
5. For the derivation of Anglo-Norman and Middle French patente (adjective) in lettre patente, see etymology 2 below.
6. The verb is derived from the noun.