General Opposites:
* Captured: If referring to a person or animal.
* Confined: If referring to something being held back.
* Restricted: If referring to something being limited.
* Contained: If referring to something being kept within bounds.
* Withheld: If referring to something being kept back or not given.
* Retained: If referring to something being kept.
Specific Opposites:
* Acquired: If referring to something being obtained.
* Purchased: If referring to something being bought.
* Seized: If referring to something being taken forcefully.
* Engaged: If referring to something being used.
* Attached: If referring to something being connected.
* Published: If referring to something being made public.
Example:
* Released: The prisoner was released from jail.
* Opposite: The prisoner was captured and returned to jail.
To choose the best opposite word, consider the context of the sentence you're using it in.