What term describes "a person who fails to return to custody following a temporary leave for a specific purpose"?

The correct term for "a person who fails to return to custody following a temporary leave for a specific purpose" is abscond. This term specifically refers to someone who has left a place they were expected to stay, often in violation of laws or regulations, such as a person on temporary leave from custody.

Considering the context of the question, absconding implies that the individual had permission or a specific condition under which they could be away from custody but chose not to return. This accurately describes the scenario outlined in the question.

Escape would usually refer to someone who has broken free from custody or confinement without permission, rather than failing to return after a temporary leave. A fugitive denotes someone who is on the run from law enforcement, typically after being accused or convicted of a crime, but does not specifically imply the context of a temporary leave. On the other hand, a runaway often refers to someone, usually a minor, who leaves their home or guardianship without permission. All these terms do not convey the specific circumstances of failing to return after a temporary leave like abscond does.