General Antonyms:
* Freedom
* Liberty
* Unrestraint
* Openness
* Flexibility
* Spontaneity
* Latitude
More Specific Antonyms:
* Expansion: If "constraint" refers to limiting size or scope.
* Permission: If "constraint" refers to a lack of authorization.
* Encouragement: If "constraint" refers to something holding back progress.
* Ease: If "constraint" refers to a feeling of tightness or restriction.
To choose the best antonym, consider the specific meaning of "constraint" in your context.