The Collaborative International Dictionary of English v.0.48:

Scavenger \Scav"en*ger\, n. [OE. scavager an officer with
   various duties, originally attending to scavage, fr. OE. & E.
   scavage. See Scavage, Show, v.]
   A person whose employment is to clean the streets of a city,
   by scraping or sweeping, and carrying off the filth. The name
   is also applied to any animal which devours refuse, carrion,
   or anything injurious to health.
   [1913 Webster]

   Scavenger beetle (Zool.), any beetle which feeds on
      decaying substances, as the carrion beetle.

   Scavenger crab (Zool.), any crab which feeds on dead
      animals, as the spider crab.

   Scavenger's daughter [corrupt. of Skevington's daughter],
      an instrument of torture invented by Sir W. Skevington,
      which so compressed the body as to force the blood to flow
      from the nostrils, and sometimes from the hands and feet.
      --Am. Cyc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

scavenger
    n 1: a chemical agent that is added to a chemical mixture to
         counteract the effects of impurities
    2: someone who collects things that have been discarded by
       others [syn: magpie, scavenger, pack rat]
    3: any animal that feeds on refuse and other decaying organic
       matter

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "scavenger":
   amphibian, aquatic, biped, canine, cannibal, carnivore,
   chimney sweep, cleanser, cosmopolite, crossing sweeper, feline,
   flue cleaner, gnawer, herbivore, insectivore, invertebrate, mammal,
   mammalian, marsupial, marsupialian, omnivore, primate, quadruped,
   reptile, rodent, ruminant, street sweeper, sweep, sweeper,
   ungulate, varmint, vermin, vertebrate, whitewing