Source : Webster's Revised Unabridged Dictionary (1913)

Detainer \De*tain"er\ (-[~e]r), n.
   1. One who detains.

   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.