fossil (n.) Look up fossil at Dictionary.com
1610s, "any thing dug up;" 1650s (adj.) "obtained by digging," from French fossile (16c.), from Latin fossilis "dug up," from fossus, past participle of fodere "to dig," from PIE root *bhedh- "to dig, pierce."

Restricted noun sense of "geological remains of a plant or animal" is from 1736; slang meaning "old person" first recorded 1859. Fossil fuel (1835) preserves the earlier, broader sense.