Strongs & TWOT on H6918 holy

Strongs: something sacred in a ceremonial or moral sense; an angel, saint, sanctuary.

Theological Word Book of the OT, #1990b: "The verb qādash in the Qal connotes the state of that which belongs to the sphere of the sacred. Thus it is distinct from the common or profane. In the Piel and Hiphil it connotes the act by which the distinction is effected. It is a denominative verb.  The word occurs in several dialects of Akkadian with the basic meanings "to be clean, pure, consecrated." In the Canaanite texts from Ugarit, the basic meaning of the word group is "holy," and it is always used in a cultic sense.  A definitive use of the term occurs in Numbers 16:38. The censers of the Korahites were regarded as holy because they had been devoted to the Lord. They were thus regarded as having entered the sphere of the sacred by virtue of cultic ritual (Numbers 16:17) and were accorded a special place in the sanctuary. The devotion of the censers seems to have created a condition of inviolable holiness that could not allow for their being treated in a common way. It seems best to see the root qdsh as serving to delineate the sphere of the "holy."

qōdesh. Apartness, holiness, sacredness, hallowed, holy (ASV, RSV, similar). The noun qōdesh connotes the concept of "holiness," i.e. the essential nature of that which belongs to the sphere of the sacred and which is thus distinct from the common or profane. This distinction is evident in Leviticus 10:10 and Ezekiel 22:26 where qōdesh occurs as the antithesis of ḥôl ("profane," "common").

There is some truth in the idea of R. Otto that the word "holy" refers to the mysterium tremendum. It speaks of God with a measure of awe. It can be used almost as a synonym of deity. "His holy name" is the name of God. The inner room of God's dwelling is called the Holy of Holies—the most holy place.

But the biblical viewpoint would refer the holiness of God not only to the mystery of his power, but also to his character as totally good and entirely without evil. Holy objects therefore are those with no cultic pollution which is symbolic of moral pollution. They are not merely dedicated, but dedicated to what is good and kept from what is evil. The separation of men from what defiles ceremonially is but typical of the holiness that is spiritual and ethical. "Be ye holy for I am holy" is quoted from the OT (1 Peter 1:16; Leviticus 19:1; Leviticus 20:7, etc.) and the so-called holiness code is heavily ethical. "Man was made in the image of God and capable of reflecting the Divine likeness. And as God reveals himself as ethically holy, he calls men to a holiness resembling his own""

Theological Wordbook of the Old Testament.