Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
massacre [ˈmæsəkər] n ма́ссовое уби́йство
vt зве́рски убива́ть (уби́ть*perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: