immolation vs ritual killing

immolation and ritual killing both are nouns.

Word	Noun	Adjective	Verb	Adverb
immolation	Yes	No	No	No
ritual killing	Yes	No	No	No

As nouns, ritual killing is a hypernym of immolation; that is, ritual killing is a word with a broader meaning than immolation:

immolation: killing or offering as a sacrifice
ritual killing: the act of killing (an animal or person) in order to propitiate a deity

Other hypernyms of immolation include sacrifice.

immolation (noun)	ritual killing (noun)
killing or offering as a sacrifice	the act of killing (an animal or person) in order to propitiate a deity