Its original root was the neuter form of the ancient Greek holokaustos (ὁλόκαυστος), from ὅλος (hólos, “whole”) + καυστός (kaustós, "burnt") or καίω (kaíō, "I burn") with the use of rough breathing to pronounce the leading h. Holokautein (ὁλοκαυτεῖν) is one of the two chief verbs of Greek sacrifice, in which the victim is utterly destroyed and burnt up, as opposed to thúesthai (θύεσθαι), to share a meal with the god and one's fellow worshippers, commensal sacrifice.
[1] Holocausts are conducted at night, without wine, and offer black-hided animals at a low altar, with their heads directed downwards; in all these they are opposed to the commensal sacrifice given to the Olympian gods.
(This distinction is between extreme types, and was somewhat exaggerated in the early twentieth century, as by Jane Harrison; considerable evidence has also been found of commensal sacrifice offered to heroes.
The animals, having first been checked to ensure they were free from disease and unblemished (a requirement of the sacrifice), were brought to the north side of the altar, and killed by either the offeror, or a priest.
The flesh of the animal was divided according to detailed instructions given by the Talmud (Tamid 31), and would then be placed on the wood on the altar (which was constantly alight due to the large number of sacrifices carried out daily), and slowly burnt.