According to the Oxford Dictionary the word holocaust means "to sacrifice oneself completely".
According to the Etymology Dictionary the word holocaust comes from "sacrifice by fire, burnt offering," from Old French holocauste (12c.), or directly from Late Latin holocaustum, from Greek holokauston "a thing wholly burnt," neuter of holokaustos "burned whole," from holos "whole" (see holo-) + kaustos.
The root -holo means "whole, entire, complete". From Greek -holos means the same.
Other words with the root -holo are Holocryptic, hologram, holograph.
The root -caustic means "burning, corrosive," from Latin causticus "burning, caustic," from Greek kaustikos "capable of burning; corrosive," from kaustos "combustible; burnt".
Other words with the root -caustic are Catacaustic, causticity.