SANTO. — From the Latin sanctus (sancire), its etymological meaning is “inviolable.” Before the word acquired its current meaning—namely, a person who during life practised all the virtues to a heroic degree, recognized as such through a canonical process conducted by ecclesiastical authority—it had several meanings, both in classical and in Christian usage.
Among the pagans, the term was used to designate everything that was consecrated to the divinity or concerned the worship of the gods, and that in any way stood under their protection. Thus the gods themselves, their images, temples, priests, the walls of the city, etc., were called s. In accordance with its etymology, the word was also used to designate everything that enjoyed the protection of the established authority, and in particular was applied to persons who, by virtue of public offices, enjoyed the personal privilege of inviolability: first and foremost, the emperor was s. By extension, someone whose moral conduct, in public and private life, was irreproachable and above all suspicion—thus manifesting moral perfection—was also called s.; consequently, s. was one who had lived in innocence, chastity, fidelity to family duties, and purity of morals. These moral qualities, in fact, derived from and were the fruit of piety toward the gods, and therefore, ultimately, those who possessed them enjoyed the protection of the gods. Because they were assimilated to the divinity, the souls of the departed, the “manes,” were also s.
(courtesy of H.E. Msgr. A. P. Frutzi)