hecatomb vs ritual killing

hecatomb and ritual killing both are nouns.

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

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

hecatomb: a great sacrifice; an ancient Greek or Roman sacrifice of 100 oxen
ritual killing: the act of killing (an animal or person) in order to propitiate a deity

Other hypernyms of hecatomb include sacrifice.

hecatomb (noun)	ritual killing (noun)
a great sacrifice; an ancient Greek or Roman sacrifice of 100 oxen	the act of killing (an animal or person) in order to propitiate a deity