General antonyms:
* Submissive
* Obedient
* Compliant
* Docile
* Yielding
* Accommodating
* Amenable
* Tractable
* Pliable
* Resigned
More specific antonyms based on context:
* Respectful (if the defiance is directed towards authority)
* Cooperative (if the defiance is towards a task or group effort)
* Apologetic (if the defiance is followed by regret)
* Reconciled (if the defiance was part of a conflict)
* Accepting (if the defiance was towards a situation)
The best antonym will depend on the specific context in which you're using the word "defiant."