Wordnet 3.0
NOUN (1)
1. 
 a great sacrifice; 
 an ancient Greek or Roman sacrifice of 100 oxen; 
The Collaborative International Dictionary of English v.0.48:
Hecatomb \Hec"a*tomb\, n. [L. hecatombe, Gr. ?; ? hundred + ?
   ox: cf. F. h['e]catombe.] (Antiq.)
   A sacrifice of a hundred oxen or cattle at the same time;
   hence, the sacrifice or slaughter of any large number of
   victims.
   [1913 Webster]
         Slaughtered hecatombs around them bleed. --Addison.
   [1913 Webster]
         More than a human hecatomb.              --Byron.
   [1913 Webster]
WordNet (r) 3.0 (2006):
hecatomb
    n 1: a great sacrifice; an ancient Greek or Roman sacrifice of
         100 oxen