'denounce' means to publicly declare (something) to be wrong or evil. You might also denounce somebody as a traitor; or some world-famous psychic as a charlatan (fraud). It implies that you disapprove, want something done to stop it or punish the person, otherwise you wouldn't take the trouble; but the important aspect of the word is that you do this publicly , as if 'telling the world'.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.