Sentence:  In Conquest's opinion, the visceral reaction to Nazism entails a verdict that it was morally worse than Stalinism, even if its eventual <WSD>hecatomb</WSD> was a less colossal one. 
Meaning of the word marked with <WSD> tags:  Any great sacrifice; a great number of people, animals or things, especially as sacrificed or destroyed; a large amount.