From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
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