1610s, "any thing dug up;" 1650s (adj.) "obtained by digging" (of coal, salt, etc.), 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 (the adjective in the sense "pertaining to fossils" is from 1660s); slang meaning "old person" first recorded 1859. Fossil fuel (1833) preserves the earlier, broader sense.
Ikhthes oryktoi "fossil fishes" were known to the Greeks, along with fossil shells on mountaintops and fossil "seaweed" in Sicilian quarries. They sometimes were taken as evidence of changing sea levels.
Ancient Greek words for "clown" were sklêro-paiktês, from paizein "to play (like a child);" or deikeliktas. Greek also had geloiastes "a jester, buffoon" (from gelao "to laugh, be merry"); there was a khleuastes "jester," but it had more of a sense of "scoffer, mocker," from khleuazo "treat with insolence." Other classical words used for theatrical clowns were related to "rustic," "peasant" (compare Latin fossor "clown," literally "laborer, digger," related to fossil).
Coulrophobia looks suspiciously like the sort of thing idle pseudo-intellectuals invent on the internet and which every smarty-pants takes up thereafter; perhaps it is a mangling of Modern Greek klooun "clown," which is the English word borrowed into Greek.
"stone presenting a fossil footprint," 1841, from Latinized form of Greek ikhnos "a track, footprint" (which is of unknown origin) + -lite. Ichnite in the same sense is from 1854. Ichnology, "scientific study of fossil footprints," is from 1837.
So numerous have been the discoveries of fossil footmarks in Europe within a few years past, and so many species occur in this country, that it will be at least convenient to have them designated by some appropriate scientific terms, and to arrange them in systematic order. I propose the term Ichnolite ... to include them all and to be the name of the Class. [Edward Hitchcock, LL.D., "Final Report on the Geology of Massachusetts," 1841]