The Collaborative International Dictionary of English v.0.48:

Slave \Slave\ (sl[=a]v), n. [Cf. F. esclave, D. slaaf, Dan.
   slave, sclave, Sw. slaf, all fr. G. sklave, MHG. also slave,
   from the national name of the Slavonians, or Sclavonians (in
   LL. Slavi or Sclavi), who were frequently made slaves by the
   Germans. See Slav.]
   1. A person who is held in bondage to another; one who is
      wholly subject to the will of another; one who is held as
      a chattel; one who has no freedom of action, but whose
      person and services are wholly under the control of
      another.
      [1913 Webster]

            Art thou our slave,
            Our captive, at the public mill our drudge?
                                                  --Milton.
      [1913 Webster]

   2. One who has lost the power of resistance; one who
      surrenders himself to any power whatever; as, a slave to
      passion, to lust, to strong drink, to ambition.
      [1913 Webster]

   3. A drudge; one who labors like a slave.
      [1913 Webster]

   4. An abject person; a wretch. --Shak.
      [1913 Webster]

   Slave ant (Zool.), any species of ants which is captured
      and enslaved by another species, especially Formica
      fusca of Europe and America, which is commonly enslaved
      by Formica sanguinea.

   Slave catcher, one who attempted to catch and bring back a
      fugitive slave to his master.

   Slave coast, part of the western coast of Africa to which
      slaves were brought to be sold to foreigners.

   Slave driver, one who superintends slaves at their work;
      hence, figuratively, a cruel taskmaster.

   Slave hunt.
      (a) A search after persons in order to reduce them to
          slavery. --Barth.
      (b) A search after fugitive slaves, often conducted with
          bloodhounds.

   Slave ship, a vessel employed in the slave trade or used
      for transporting slaves; a slaver.

   Slave trade, the business of dealing in slaves, especially
      of buying them for transportation from their homes to be
      sold elsewhere.

   Slave trader, one who traffics in slaves.
      [1913 Webster]

   Syn: Bond servant; bondman; bondslave; captive; henchman;
        vassal; dependent; drudge. See Serf.
        [1913 Webster]

WordNet (r) 3.0 (2006):

slave driver
    n 1: a cruel employer who demands excessive work from the
         employees [syn: slave driver, Simon Legree]
    2: a supervisor of slaves at work

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "slave driver":
   Big Brother, Simon Legree, absolute monarch, absolute ruler,
   all-powerful ruler, arrogator, auditor, autarch, autocrat,
   boatswain, boss, caesar, chief, commissar, comptroller, controller,
   czar, despot, dictator, disciplinarian, driver, duce,
   floor manager, floorman, floorwalker, foreman, gaffer, ganger,
   hard master, head, headman, inspector, martinet, monitor,
   noncommissioned officer, oligarch, oppressor, overman, overseer,
   pharaoh, proctor, sirdar, stickler, straw boss, subforeman, super,
   superintendent, supervisor, surveyor, taskmaster, tyrant, usurper,
   visitor, warlord