early 12c. as an adjective, seinte, "holy, divinely inspired, worthy of worship," used before proper names (Sainte Marian Magdalene, etc.), from Old French saint, seinte "holy, pious, devout," from Latin sanctus "holy, consecrated," past participle of sancire "consecrate" (see sacred). It displaced or altered Old English sanct, which is directly from Latin sanctus.
From an adjective prefixed to the name of a canonized person, it came to be used in English by c. 1200 as a noun, "a specific canonized Christian," also "one of the elect, a member of the body of Christ, one consecrated or set apart to the service of God," also in an Old Testament sense "a pre-Christian prophet."
It is attested by late 13c. as "moral or virtuous person, one who is pure or upright in heart and life."
The adjectives also were used as nouns in Late Latin and Old French: "a saint; a holy relic." The Latin word also is the source of Spanish santo, santa, Italian san, etc., and also ultimately the source of the word in most Germanic languages (Old Frisian sankt, Dutch sint, German Sanct).
Perhaps you have imagined that this humility in the saints is a pious illusion at which God smiles. That is a most dangerous error. It is theoretically dangerous, because it makes you identify a virtue (i.e., a perfection) with an illusion (i.e., an imperfection), which must be nonsense. It is practically dangerous because it encourages a man to mistake his first insights into his own corruption for the first beginnings of a halo round his own silly head. No, depend upon it; when the saints say that they—even they—are vile, they are recording truth with scientific accuracy. [C.S. Lewis, "The Problem of Pain," 1940]
"to enroll (someone) among the saints," c. 1200, in beon isontet "be sainted," from saint (n.) or from Old French santir. Related: Sainted; sainting.
by 1829 in reference to the socialistic system promoted by Claude Henri, Comte de Saint-Simon (1760-1825) of France.
French, literally "feast of All Saints" (Nov. 1), from tous, plural of tout "all" + saint "saint."
surname and masc. proper name, from Irish/Gaelic Naomhin "little saint."
the Spanish title for a female saint, feminine singular of san, from Latin sanctus (see saint (n.)). As in Santa Lucia, Santa Maria, and in many toponyms in the U.S. West, such as Santa Ana ("Saint Anne"), the California mountain range, also extended to the hot, strong, dry wind that blows from it.
before vowels hagi-, word-forming element meaning "of a saint, saintly, holy," from Greek hagios "sacred, devoted to the gods" (of things), "holy, pure" (of persons), in Ecclesiastical Greek, "a saint," which is perhaps from PIE *yag- "to worship, reverence" (source also of Greek agnos "chaste," Sanskrit yajati "reveres (a god) with sacrifices, worships," Old Persian ayadana "temple").