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