The Collaborative International Dictionary of English v.0.48:

genocide \gen"o*cide\ n.
   The systematic killing of a racial or cultural group; as, the
   Nazi genocide of Jews left few in Germany or Poland after
   World War II.

   Syn: race murder, racial extermination.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

genocide
    n 1: systematic killing of a racial or cultural group [syn:
         genocide, race murder, racial extermination]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "genocide":
   aborticide, atrocity, bloodbath, breach, carnage, crime,
   crime against humanity, deadly sin, decimation, delinquency,
   dereliction, enormity, error, evil, failure, fault, felony,
   final solution, fratricide, fungicide, germicide, guilty act,
   heavy sin, herbicide, holocaust, homicide, impropriety,
   indiscretion, inexpiable sin, infanticide, iniquity, injury,
   injustice, insecticide, lapse, malefaction, malfeasance, malum,
   mass destruction, mass murder, massacre, matricide, microbicide,
   minor wrong, misdeed, misdemeanor, misfeasance, mortal sin,
   nonfeasance, offense, omission, outrage, parricide, patricide,
   peccadillo, peccancy, pesticide, pogrom, race extermination,
   race-murder, regicide, rodenticide, saturnalia of blood, sin,
   sin of commission, sin of omission, sinful act, slip, sororicide,
   suicide, tort, transgression, trespass, trip, unutterable sin,
   uxoricide, venial sin, vermicide, wholesale murder, wrong