Middle English holinesse, from Old English halignis "state or character of being holy, sanctity, religion; holy thing;" see holy + -ness. Compare Old High German heilagnissa. As title of the Pope (mid-15c. in English), it translates Latin sanctitas (until c. 600 also applied to bishops).
hole-in-the-wall
holey
holiday
holier-than-thou
holily
holiness
holism
holistic
holla
Holland
hollandaise