from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A fossilized material in shale and other sedimentary rock that yields oil upon heating.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. any organic matter present in a sedimentary rock that is insoluble in organic solvents; the precursor of oil and natural gas
Greek kēros, wax + -gen.(American Heritage® Dictionary of the English Language, Fourth Edition)