The Etymology of Holy
Holy is one of the most quietly philosophical words in English. Its Proto-Indo-European root *kailo- meant whole, uninjured, intact, of good omen — and from that single seed five English words sprouted: holy, whole, hale, health, and heal. Sanctity, in this old Germanic conception, was not separateness but integrity: a holy thing was an unbroken thing, and to heal was to make whole again. Pagan Germanic religion likely used hālig before Christian missionaries adopted it to translate Latin sanctus around the 7th century. The Christian sense gradually crowded out the older meaning; whole branched off to keep the secular sense; and hale survived in archaic phrases like hale and hearty. Holy Week, holy water, holy ghost, and holy of holies are all calques (loan-translations) from Greek and Latin Christian usage, fitted onto an older Germanic word that already meant inviolable.