"the state of being evident," 1650s, from patent (adj.) + abstract noun suffix -cy.
Entries linking to patency
patent adj.
late 14c., "granting a right, privilege, or power," in letters patent, literally "open letter" (see patent (n.)), from Old French patente "open," from Latin patentem (nominative patens) "open, lying open," present participle of patere "lie open, be open" (from PIE root *pete- "to spread"). The sense of "open to view, plain, clear" is recorded from c. 1500. As an adverb, "openly, publicly, unmistakably," mid-15c. Related: Patently.
-cy
abstract noun suffix of quality or rank, from Latin -cia, -tia, from Greek -kia, -tia, from abstract ending -ia (see -ia) + stem ending -c- or -t-. The native correspondents are -ship, -hood.