privity (n.)

early 13c., "a thing kept hidden or secret," also "privacy, private life; secrecy," from Old French privité, priveté "privacy; a secret, private matter" (c. 1200), from prive "private," from Latin privus "set apart, belonging to oneself" (see private (adj.)).

From 1550s as "participation in the knowledge of something secret;" from 1520s as a legal term in feudal land tenure. Privities "private parts" is attested by late 14c.