The Collaborative International Dictionary of English v.0.48:

Bloodsucker \Blood"suck`er\, n.
   1. (Zool.) Any animal that sucks blood; esp., the leech
      (Hirudo medicinalis), and related species.
      [1913 Webster]

   2. One who sheds blood; a cruel, bloodthirsty man; one guilty
      of bloodshed; a murderer. [Obs.] --Shak.
      [1913 Webster]

   3. A hard and exacting master, landlord, or money lender; an
      extortioner.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bloodsucker
    n 1: carnivorous or bloodsucking aquatic or terrestrial worms
         typically having a sucker at each end [syn: leech,
         bloodsucker, hirudinean]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "bloodsucker":
   barnacle, bedbug, blackmailer, extortioner, extortionist,
   freeloader, hanger-on, harpy, leech, lounge lizard, moocher,
   mosquito, parasite, predator, profiteer, racketeer, raptor,
   scrounge, scrounger, shakedown artist, shark, spiv, sponge,
   sponger, sucker, tick, vampire, vulture, wood tick