from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An organism adapted to living in conditions of extreme temperature, pressure, or chemical concentration, as in highly acidic or salty environments.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An organism that lives under extreme conditions of temperature, salinity etc; commercially important as a source of enzymes that operate under similar conditions.
extrem(e) + -o- + -phile.(American Heritage® Dictionary of the English Language, Fourth Edition)
From extreme + -o- + -phile. (Wiktionary)