General antonyms:
* Compliance
* Obedience
* Submission
* Acquiescence
* Submissiveness
* Concession
* Yielding
* Resignation
* Acceptance
* Amenability
More specific antonyms:
* Cooperation (if defiance is directed at a group or authority)
* Respect (if defiance is directed at a person or institution)
* Agreement (if defiance is about a particular decision or idea)
The best antonym for defiance depends on the specific context.