HOLY, sacred, devoted or set apart for religious worship or observance; a term characteristic of the attributes of perfection and sinlessness of the Persons of the Trinity, as the objects of human worship and reverence, and hence transferred to those human persons who, either by their devotion to a spiritual ascetic life or by their approximation to moral perfection, are considered worthy of reverence. The word in Old English was halig, and is common to other Teutonic languages; cf. Ger. and Dutch heilig, Swed. helig, Dan. hellig. It is derived from hal, hale, whole, and cognate with " health." The New English Dictionary suggests that the sense- development may be from "whole," i.e.. inviolate, from "health, well-being," or from " good-omen," " augury." It is impossible to get behind the Christian uses, in which from the earliest times it was employed as the equivalent of the Latin sacer and sanclus.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)