*detainer*

n. 1. One who detains. [ 1913 Webster ]

2. (Law) (a) The keeping possession of what belongs to another; detention of what is another's, even though the original taking may have been lawful. Forcible detainer is indictable at common law. (b) A writ authorizing the keeper of a prison to continue to keep a person in custody. [ 1913 Webster ]