What is a hectatomb?

It's hecatomb. hecatomb (ˈhɛkəˌtəʊm; -ˌtuːm)

n

1. (Historical Terms) (in ancient Greece or Rome) any great public sacrifice and feast, originally one in which 100 oxen were sacrificed

2. a great sacrifice

[C16: from Latin hecatombē, from Greek hekatombē, from hekaton hundred + bous ox]