Dictionary.com
definitions

extremophile

noun
  1. a microbe that lives in an environment once thought to be uninhabitable, for example in boiling or frozen water
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
extremophile in Science

extremophile

[ĭk-strē′mə-fīl′]
  1. An organism adapted to living in conditions of extreme temperature, pressure, or chemical concentration, as in highly acidic or salty environments. Many extremophiles are unicellular organisms known as archaea.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.