Anointing of the sick, known also by other names such as unction, is a form of religious anointing or "unction" (an older term with the same meaning) for the benefit of a sick person. It is practiced by many Christian churches and denominations.
Anointing of the sick was a customary practice in many civilizations, including among the ancient Greeks and early Jewish communities. The use of oil for healing purposes is referred to in the writings of Hippocrates.[1][2]
^P. J. Hartin, Daniel J. Harrington James -- 2003 Page 267 "Anointing of the sick was a customary practice in both the Hellenistic and Jewish worlds. The use of oil for healing purposes is referred to in the writings of Hippocrates: "Exercises in dust differ from those in oil thus. Dust is cold, oil is warm."
^John LightfootHoræ hebraicæ et talmudicæ: Hebrew and Talmudical exercitations Volume 2 - Page 155 "On the ninth day of the month Ab, and in the public fasts, anointing for dress is forbid; anointing not for dress is allowed." [Hebrew text] They anointed themselves often, not for excess, or bravery, or delight, but for the healing of some disease, "
^Oxford Dictionary of the Christian Church (Oxford University Press 2005 ISBN978-0-19-280290-3), article "unction"