General Antonyms:
* Conceal: To hide or keep secret.
* Suppress: To prevent from being known or expressed.
* Withhold: To refuse to give or reveal.
* Deny: To state that something is not true.
Specific Antonyms:
* Recant: To formally withdraw a statement or belief.
* Retract: To take back something said or written.
* Disavow: To deny responsibility for something.
* Disprove: To show that something is false.
Examples:
* Instead of declaring their love, they concealed their feelings.
* The government suppressed the news of the disaster.
* He withheld information about the incident.
* She denied ever having met him.
The best antonym for "declare" will depend on the specific situation and what you want to convey.