patentyoudaoicibaDictYouDict[patent 词源字典]
patent: [14] Etymologically, patent means simply ‘open’. Its ultimate source is patēns, the present participle of the Latin verb patēre ‘be open’ (a relative of English fathom and petal). It was used particularly in the term letters patent, which denoted an ‘open letter’, particularly an official one which gave some particular authorization, injunction, etc.

It soon came to be used as a noun in its own right, signifying such a letter, and by the end of the 16th century it had acquired the meaning ‘exclusive licence granted by such a letter’. This gradually passed into the modern sense ‘official protection granted to an invention’.
=> fathom, petal[patent etymology, patent origin, 英语词源]
patent (n.)youdaoicibaDictYouDict
late 14c., "open letter or document from some authority," shortened form of Anglo-French lettre patent (also in Medieval Latin (litteræ) patentes), literally "open letter" (late 13c.), from Old French patente (see patent (adj.).
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]
Meaning "a license covering an invention" is from 1580s.
patent (v.)youdaoicibaDictYouDict
"to obtain right to land," 1670s, from patent (n.). 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. Related: Patented; patenting.
patent (adj.)youdaoicibaDictYouDict
late 14c., in letters patent, literally "open letter," from Old French patente, from Latin patentum (nominative patens) "open, lying open," present participle of patere "lie open, be open," from PIE *pete- "to spread" (see pace (n.)). Sense of "open to view, plain, clear" is first recorded c. 1500. Related: Patently.