Source : Webster's Revised Unabridged Dictionary (1913)

Jailer \Jail"er\, n. [OE. jailer, gailer, OF. geolier, F.
   ge[^o]lier. See {Jail}.]
   The keeper of a jail or prison. [Written also {jailor},
   {gaoler}.]

Source : WordNet®

jailer
     n : someone who guards prisoners [syn: {prison guard}, {jailor},
          {gaoler}, {screw}, {turnkey}]