Origin and history of secrecy

late 14c., primacie, "preeminent position, supremacy, condition of being first in order, power, or importance," from Old French primacie (14c.; Modern French primatie) and directly from Medieval Latin primatia "office of a church primate" (12c.), from Late Latin primas (genitive primatis) "principal, chief, of the first rank," from primus "first" (see prime (adj.)).

late 14c., "set or kept apart, hidden, concealed," from French secret, adjective use of noun, from Latin secretum "a secret, a hidden thing" (see secret (n.)). 

Secret agent is recorded by 1715; secret service is from 1737, "department of a government concerned with counterfeiting and other political and civil offenses done in secrecy;" secret police is by 1823. Secret weapon is by 1590s.

suffix of Latin origin, via Old French, used in forming abstract nouns denoting quality or condition from adjectives derived from Latin (safety, surety, loyalty, poverty; in city it is hardly recognizable); Middle English -tie, -te, from Old French -te (Modern French -té).

This is from Latin -tatem (nominative -tas, genitive -tatis), cognate with Greek -tes, Sanskrit -tati-. The cognate suffix in Spanish is -dad. So commonly preceded by a stem-vowel in -i- that -ity has become a living English formative.