Dictionary Definition

hecatomb n : a great sacrifice; an ancient Greek or Roman sacrifice of 100 oxen

User Contributed Dictionary

From hecatombe, from ἑκατόμβη, from ἑκατόν + βοῦς.

In ancient Greece or Rome, a great feast and public sacrifice to the gods, originally of a hundred oxen.
Hence loosely, any great sacrifice; a great number of people, animals or things; a large amount.
- 2006, Karen Armstrong, The Great Transformation, Atlantic Books 2007, p. 31-2:
  
  During the royal hunt, the Shang killed wild beasts with reckless abandon, and consumed hecatombs of domestic animals at a bin banquet or a funeral.

In Ancient Greece, a Hecatomb (Ancient Greek / hekatómbê) was a sacrifice to the gods of 100 cattle (hecaton = one hundred).

In the Iliad hecatombs are described formulaically. The following is one instance, from Samuel Butler's translation:

[T]hey ranged the holy hecatomb all orderly round the altar of the god. They washed their hands and took up the barley-meal to sprinkle over the victims [cattle], while [the priest] lifted up his hands and prayed aloud on their behalf.
...
When they had done praying and sprinkling the barley-meal, they drew back the heads of the victims and killed and flayed them. They cut out the thigh-bones, wrapped them round in two layers of fat, set some pieces of raw meat on the top of them, and then [the priest] laid them on the wood fire and poured wine over them, while the young men stood near him with five-pronged spits in their hands. When the thigh-bones were burned and they had tasted the inward meats, they cut the rest up small, put the pieces upon the spits, roasted them till they were done, and drew them off: then, when they had finished their work and the feast was ready, they ate it, and every man had his full share, so that all were satisfied. As soon as they had had enough to eat and drink, pages filled the mixing-bowl with wine and water and handed it round, after giving every man his drink-offering.

Thus all day long the young men worshipped the god with song, hymning him and chaunting the joyous paean, and the god took pleasure in their voices[.]