The proper meaning of the Hebrew word for holy, kadosh, is matter of uncertainty. It may come from a root signifying to shine. (So Gesenius, Oehler, Fuerst, and formerly Delitzsch, on Heb. ii.11.) Or from another denoting new and bright (Diestel), or an Arabic form meaning to cut, to separate. (So Delitzsch now, on Ps. xxii.4.) Whatever the root be, the chief idea appears to be not only separate or set apart, for which the Hebrew has entirely different words, but that by which a thing that is separated from others for its worth is distinguished above them. It indicates not only separation as an act or fact, but the superiority or excellence in virtue of which, either as already possessed or sought after, the separation takes place.

In his Lexicon of New Testament Greek, Cremer has an exhaustive article on the Greek hagios, pointing out how holiness is an entirely Biblical idea, and 'how the scriptural conceptions of God's Holiness, notwithstanding the original affinity, is diametrically opposite to all the Greek notions; and how, whereas these very views of holiness exclude from the gods all possibility of love, the scriptural conception of holiness unfolds itself only when in closest connection with Divine love.' It is a most suggestive thought that we owe both the word and the thought distinctly to revelation. Every other attribute of God has some notion to correspond with it in the human mind: the thought of holiness is distinctly Divine. Is not this the reason that, though God has so distinctly in the New Testament called His people holy ones, the word holy has so little entered into the daily language and life of the Christian Church?