WordWeb Online

1. Corrupt morally or by intemperance or sensuality
   "Socrates was accused of vitiating young men";
   - corrupt, pervert, subvert, demoralize, demoralise [Brit], debauch, debase, profane, deprave, misdirect
    
2. Make imperfect
   - mar, impair, spoil, deflower, pollute
    
3. Take away the legal force of or render ineffective
   "vitiate a contract";
   - invalidate, void

Derived forms: vitiated, vitiates, vitiating

Type of: alter, change, damage, modify