He who has knowledge of the most secret parts of everything, and knows their inner meanings. The omniscient knows, witnesses, and sees all things and is aware of all conditions anywhere, anytime, hidden, visible or invisible, all news of His creature universe or the Hereafter.
“O mankind! We created you from a single (pair) of a male and a female, and made you into nations and tribes, that ye may know each other (not that ye may despise each other). Verily the most honoured of you in the sight of Allah is (he who is) the most righteous of you. And Allah has full Knowledge and IS WELL- ACQUAINTED (WITH ALL THINGS).”
(49:13) The Holy Quran
From the root kh-b-r with the classical Arabic connotations: to know, or be aware of the real inner nature of something to know the reality of something