Option 1: Concur -> means to agree with something, which is opposite to denounce.
Option 2: Criticise -> means to express disapproval or condemn, similar to denounce.
Option 3: Defend -> means to protect or support, which is opposite to denounce.
Option 4: Eulogise -> means to praise highly, which is opposite to denounce.
Hence, Option 2: Criticise -> "Denounce" means to publicly condemn or criticize harshly, making "criticise" the closest synonym among the given options -> correct