* Affirm: This means to state something is true, the opposite of denying it.
* Acknowledge: This means to recognize something as true or existing.
* Admit: This means to confess or accept responsibility for something.
* Confirm: This means to prove something is true.
* Grant: This means to allow or give permission for something.
The best opposite word will depend on the specific situation and the meaning of "deny" in that context.