1540s, "quality of being real, objective reality," from French réalité and directly from Medieval Latin realitatem (nominative realitas), from Late Latin realis (see real (adj.)). Also compare realty, which was the older form of the word in the sense of "reality" (mid-15c.).
Meaning "real existence, what is real, the aggregate of all that is real" is from 1640s; that of "the real state (of something)" is from 1680s. Sometimes 17c.-18c. it also meant "sincerity." Reality-based is attested from 1960, in marriage counseling. Reality television is attested from 1991.