In a literal sense:
* Expand: This is the most general opposite, meaning to make something larger or wider.
* Dilate: This is often used for specific things like pupils or blood vessels.
* Loosen: This implies a release of pressure or tightness.
In a figurative sense:
* Liberate: This refers to freeing something from constraints.
* Empower: This suggests giving someone more freedom or authority.
* Encourage: This implies giving someone the confidence or support to act freely.
Example:
* Literal: The constricted pipe was expanded to allow more water flow.
* Figurative: The strict rules liberated the students from boredom.
The best opposite word will depend on the specific context and the intended meaning.